feat: tsconfig.json by default if tsconfig.build.json not exist

[zanminkian]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Other... Please describe:

What is the current behavior?

Some simple and small project only use tsconfig.json and have no tsconfig.build.json on the root of project. It will throw an error if developer execute nest build on the root. They have to execute nest build -p tsconfig.json, which is not simple and clean. Moreover, some developer who is new to TypeScript only know tsconfig.json and don't know what is tsconfig.build.json.

What is the new behavior?

Execute nest build will not throw error if there is only tsconfig.json.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[zanminkian]

Unit tests in CI will fail because of some cases will fail on master branch. Seems not caused by this PR.

[kamilmysliwiec]

LGTM