[GSoC RFC PATCH v2 0/7] repo-info: add new command for retrieving repository info

Hi!

This is the second version of the repo-info RFC, and these are the main changes introduced since v1:

• The plaintext format now returns its fields in a key=value format

• The tests were renumbered to t1900, since it's a new command (the previous was t1518, following the numbering of rev-parse)

• The test function 'test_repo_info' now has a docstring, and it is more flexible for using more complex repository initializations

• The flag --allow-empty is now introduced in its own commit

• The plaintext and the JSON formats are now introduced in their own commits

• The JSON format tests, which depends on the Perl's JSON module, are now marked with the PERLJSON lazy prereq, being skipped in environments that don't have that module installed

Some things pointed in the last review weren't implemented as I prefer to do them in another iteration of repo-info after having its basic functionality working:

• Remove the dependency on 'the_repository' when calling 'is_bare_repository'

• Add a --batch-command mode, based on the --bath-command flag of cat-file, introduced in 440c705e (cat-file: add --batch-command mode, 2022-02-18)

• Use the category as key instead of only accepting category.key. In the current patchset, git repo-info layout would equivalent to git repo-info layout.bare layout.shallow

I'm cc'ing my mentors and everyone that answered me in v1 and my GSoC blog. I'm still open to any suggestions, requests and questions that you may have!