feat: --silence-no-projects to comments with -d and -p

[Dawnflash]

what

• Makes the SilenceNoProjects flag ignore targeted projects (-d, -p flags) if no configured projects match the target
• This only applies if projects are defined at repo-level to cooperate with the no-projects setup.
• The flag effectively restricts the server to defined projects (unless none are defined), which is a mildly breaking feature
• Adds interaction with SilenceNoProjects to the import command as it is currently lacking it

why

• The SilenceNoProjects flag is effective at silencing non-targeted commands like atlantis plan but falls flat with targeted commands like atlantis plan -d mydir.
• Since the purpose of this flag is mainly serving multi-atlantis setups with fully distinct project sets, it is quite undesirable to have an "unused" server (one with 0 project matches) reply with "404, have you run plan?" or similar since it's not expected to run anything in the first place.
• When -p and -d are used in this setup, we only ever want one Atlantis server to handle the command

tests

• I added a unit test to the command builder internal tests that tests that my use-case actually ignores the handed project as opposed to a control case.
• two more tests are added to cover the targeted-but-not-matched plan use-case and interaction with the import command

references

• closes Feature request: flag to disable plan/apply on projects not included in atlantis.yaml #1876

[Dawnflash]

I updated the import cmd to react to the flag and tried covering more use-cases, especially those in the linked issue.
I tried covering the basics with tests but it doesn't test every possibility.

Now the flag locks the server down on defined projects (it will silently ignore anything else) which is backwards-incompatible (the flag hasn't behaved this way until now). Maybe a new flag could be introduced instead but I haven't figured out how to call it.

[GenPage]

@Dawnflash I approved the test runs, can you rebase?

[nitrocode]

Thank you for the PR @Dawnflash !

cc @runatlantis/maintainers for another review

[jamengual]

LGTM

[jamengual]

Thanks again @Dawnflash for the contribution

[nitrocode]

@Dawnflash there seems to be a linting issue. Let's fix that before merging.

reviewdog: found at least one result in diff
  reviewdog: Reporting results for "golangci-lint"
  Error: [golangci-lint] reported by reviewdog 🐶
  Error return value of `db.UpdatePullWithResults` is not checked (errcheck)
  
  Raw Output:
  server/events/apply_command_runner_test.go:166:29: Error return value of `db.UpdatePullWithResults` is not checked (errcheck)
  				db.UpdatePullWithResults(modelPull, []command.ProjectResult{
  				                        ^
  Error: [golangci-lint] reported by reviewdog 🐶
  Error return value of `db.UpdatePullWithResults` is not checked (errcheck)
  
  Raw Output:
  server/events/plan_command_runner_test.go:104:29: Error return value of `db.UpdatePullWithResults` is not checked (errcheck)
  				db.UpdatePullWithResults(modelPull, []command.ProjectResult{
  				                        ^

[Dawnflash]

Oops, I fixed that.

[nitrocode]

Thank you again!! This will be available in the dev tag (once the build finishes). Please use that tag if possible to keep testing this feature.