feat: implement stats per linter with a flag

[mostafa]

In this PR I added a flag that enables basic stats collection and printing per linter using the --show-stats-per-linter flag to the run subcommand. This only prints the stats to the terminal after running all the linters.

Note to the reviewers:
I tried implementing it using e.runAnalysis to return the stats from the run.Run, yet it made things more complicated. I can still do it if you prefer that approach and I'd be happy to have your feedback. Also, I can either update the printers.Print interface to accept the stats or add a extra field (somewhere), so that the stats are printed based on the formatter used, and not just to the terminal.

Closes #2924.

[boring-cyborg]

Hey, thank you for opening your first Pull Request !

[CLAassistant]

All committers have signed the CLA.

[ldez]

Hello,

I made some modifications:

• Replaced --show-stats-per-linter by --show-stats.

• Changed the output:

  Before

  Stats per linter:
    goconst: 1
    tagalign: 1
    inamedparam: 5
    musttag: 1
    perfsprint: 50
    nolintlint: 1
    typecheck: 2
    gofumpt: 1
    protogetter: 20
    testifylint: 50
  

  Note: the order of linters is not deterministic (because of a map).

  Stats per linter:
    no issues
  

  After

  132 issues:
  * goconst: 1
  * gofumpt: 1
  * inamedparam: 5
  * musttag: 1
  * nolintlint: 1
  * perfsprint: 50
  * protogetter: 20
  * tagalign: 1
  * testifylint: 50
  * typecheck: 2
  

  Note: the order of linters is deterministic (alphabetic order).

  0 issues.
  

• Added the option to the documentation.

[mostafa]

@ldez

Awesome! Thanks! 🙏

[ldez]

Thank you for your contribution to golangci-lint.
Your PR will benefit many users.

[mostafa]

@ldez

Thanks for tending to it so quickly! 🙏

[alexandear]

Do we need to add a unit or integration test?

[ldez]

no need for now, we will wait for users' feedback before doing something because the current implementation is simple and it can evolve with feedback.