feat: support templates for gitlab_urls config

Background
---
When a git repository is hosted in multiple GitLab instances the
`.goreleaser.yml` needs to take in consideration both APIs endpoints. At
the moment it defaults to GitLab.com and you can override it with
`gitlab_urls` however this forces you to only support 1 GitLab instance.

We need this for
https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/14122
where we have a tool that is developed on GitLab.com but then mirrored
to an internal GitLab instance since we need it to operate GitLab.com
even when it's down.

Solution
---
Support templates like `{{ .Env.CI_SERVER_URL }}` for the
`gitlab_urls.api` and `gitlab_urls.download` so it can use envirionment
variables.

internal/client/gitlab.go

@@ -35,7 +35,12 @@ func NewGitLab(ctx *context.Context, token string) (Client, error) {
 		}),
 	}
 	if ctx.Config.GitLabURLs.API != "" {
-		options = append(options, gitlab.WithBaseURL(ctx.Config.GitLabURLs.API))
+		apiURL, err := tmpl.New(ctx).Apply(ctx.Config.GitLabURLs.API)
+		if err != nil {
+			return nil, fmt.Errorf("templating GitLab API URL: %w", err)
+		}
+
+		options = append(options, gitlab.WithBaseURL(apiURL))
 	}
 	client, err := gitlab.NewClient(token, options...)
 	if err != nil {
@@ -326,7 +331,11 @@ func (c *gitlabClient) Upload(
 		return err
 	}
 
-	gitlabBaseURL := ctx.Config.GitLabURLs.Download
+	gitlabBaseURL, err := tmpl.New(ctx).Apply(ctx.Config.GitLabURLs.Download)
+	if err != nil {
+		return fmt.Errorf("templating GitLab Download URL: %w", err)
+	}
+
 	linkURL := gitlabBaseURL + "/" + projectDetails.PathWithNamespace + projectFile.URL
 	name := artifact.Name
 	filename := "/" + name

internal/client/gitlab_test.go

@@ -1,8 +1,16 @@
 package client
 
 import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"strings"
 	"testing"
 
+	"github.com/goreleaser/goreleaser/internal/artifact"
 	"github.com/goreleaser/goreleaser/pkg/config"
 	"github.com/goreleaser/goreleaser/pkg/context"
 	"github.com/stretchr/testify/require"
@@ -30,3 +38,137 @@ func TestGitLabReleaseURLTemplate(t *testing.T) {
 	expectedURL := "https://gitlab.com/owner/name/-/releases/{{ .Tag }}/downloads/{{ .ArtifactName }}"
 	require.Equal(t, expectedURL, urlTpl)
 }
+
+func TestGitLabURLsAPITemplate(t *testing.T) {
+	tests := []struct {
+		name     string
+		apiURL   string
+		wantHost string
+	}{
+		{
+			name:     "default_values",
+			wantHost: "gitlab.com",
+		},
+		{
+			name:     "speicifed_api_env_key",
+			apiURL:   "https://gitlab.example.com",
+			wantHost: "gitlab.example.com",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			envs := []string{}
+			gitlabURLs := config.GitLabURLs{}
+
+			if tt.apiURL != "" {
+				envs = append(envs, fmt.Sprintf("GORELEASER_TEST_GITLAB_URLS_API=%s", tt.apiURL))
+				gitlabURLs.API = "{{ .Env.GORELEASER_TEST_GITLAB_URLS_API }}"
+			}
+
+			ctx := context.New(config.Project{
+				Env:        envs,
+				GitLabURLs: gitlabURLs,
+			})
+
+			client, err := NewGitLab(ctx, ctx.Token)
+			require.NoError(t, err)
+
+			gitlabClient, ok := client.(*gitlabClient)
+			require.True(t, ok)
+
+			require.Equal(t, tt.wantHost, gitlabClient.client.BaseURL().Host)
+		})
+	}
+
+	t.Run("no_env_specified", func(t *testing.T) {
+		ctx := context.New(config.Project{
+			GitLabURLs: config.GitLabURLs{
+				API: "{{ .Env.GORELEASER_NOT_EXISTS }}",
+			},
+		})
+
+		_, err := NewGitLab(ctx, ctx.Token)
+		require.Error(t, err)
+	})
+}
+
+func TestGitLabURLsDownloadTemplate(t *testing.T) {
+	tests := []struct {
+		name        string
+		downloadURL string
+		wantURL     string
+		wantErr     bool
+	}{
+		{
+			name:    "empty_download_url",
+			wantURL: "/",
+		},
+		{
+			name:        "download_url_template",
+			downloadURL: "{{ .Env.GORELEASER_TEST_GITLAB_URLS_DOWNLOADS }}",
+			wantURL:     "https://gitlab.example.com/",
+		},
+		{
+			name:        "download_url_template_invalid_value",
+			downloadURL: "{{ .Eenv.GORELEASER_NOT_EXISTS }}",
+			wantErr:     true,
+		},
+		{
+			name:        "download_url_string",
+			downloadURL: "https://gitlab.acme.example.com",
+			wantURL:     "https://gitlab.acme.example.com/",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				defer fmt.Fprint(w, "{}")
+				defer w.WriteHeader(http.StatusOK)
+				defer r.Body.Close()
+
+				if !strings.Contains(r.URL.Path, "assets/links") {
+					io.Copy(io.Discard, r.Body)
+					return
+				}
+
+				b, err := io.ReadAll(r.Body)
+				require.NoError(t, err)
+				reqBody := map[string]interface{}{}
+				json.Unmarshal(b, &reqBody)
+				require.Equal(t, tt.wantURL, reqBody["url"])
+			}))
+			defer srv.Close()
+
+			ctx := context.New(config.Project{
+				Env: []string{
+					fmt.Sprintf("GORELEASER_TEST_GITLAB_URLS_DOWNLOADS=%s", "https://gitlab.example.com"),
+				},
+				Release: config.Release{
+					GitLab: config.Repo{
+						Owner: "test",
+						Name:  "test",
+					},
+				},
+				GitLabURLs: config.GitLabURLs{
+					API:      srv.URL,
+					Download: tt.downloadURL,
+				},
+			})
+
+			tmpFile, err := os.CreateTemp(t.TempDir(), "")
+			require.NoError(t, err)
+
+			client, err := NewGitLab(ctx, ctx.Token)
+			require.NoError(t, err)
+
+			err = client.Upload(ctx, "1234", &artifact.Artifact{Name: "test", Path: "some-path"}, tmpFile)
+			if tt.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+		})
+	}
+}