[1/x] Prepare code sprint and implement repository type detection

Description

This PR is part of our code sprint: https://trello.com/c/hU27QHob/3134-rdeb-sprint-tracker

The whole changeset is: [1/x] Prepare code sprint and implement repository type detection [2/x] Add debian mirroring support to RMT

Implementations in this PR:

Move current mirror.rb into mirror/repomd.rb and make CLI and everything working with the new layout
Implement detect_repository_type (see: https://github.com/SUSE/rmt/pull/1056/files#diff-ab471d2d1e1090f261618b78f4d678e711afb8063a7303187375a3bbe3bee075R15)

The repository type is not yet used in any way and is only there for future use.

How to test this pull request:

Make sure mirroring is working as expected

$ bin/rmt-cli mirror
# Expect: mirroring to work normally

Test repository type detection

# Sync any of our test accounts or our RMT reference account
$ rails c
> debian = Repository.find_by(name: 'Debian-10-SUSE-Manager-Tools')
> repomd = Repository.find_by(name: 'SLE-Product-SLED15-SP6-Pool')
> debian_mirror = RMT::Mirror.new(repository: debian, logger: nil, base_dir: '/tmp')
> repomd_mirror = RMT::Mirror.new(repository: repomd, logger: nil, base_dir: '/tmp')

> repomd_mirror.detect_repository_type
# expect: to return :repomd

> debian_mirror.detect_repository_type
# expect: to return :debian

Thanks for reviewing this pull request!

If you have any question please do not hesitate to approach me! :rocket:

SUSE / rmt

[1/x] Prepare code sprint and implement repository type detection #1056

Description