Secure DefaultServerTLSConfig

Followup of onflow#944: DefaultServerTLSConfig is unused, but will be in a further PR (onflow#989)
Fix an insecurity, allowing for a TLS [MinVersion == 1.0](https://github.com/golang/go/blob/e3176bbc3ec7ab3889f02432f6fd088c90fc12dd/src/crypto/tls/common.go#L685) (CWE 295)
Use gosec (through golang-ci) to prohibit that error.

.golangci.yml

@@ -9,6 +9,13 @@ linters-settings:
     # it's a comma-separated list of prefixes
     local-prefixes: github.com/onflow/flow-go
 
+  gosec:
+    # To select a subset of rules to run.
+    # Available rules: https://github.com/securego/gosec#available-rules
+    includes:
+      - G402
+
 linters:
   enable:
     - goimports
+    - gosec