Custom repo support for AzLinux

[adamperlin]

What this PR does / why we need it:
This PR adds custom repo support for Azure Linux. Jammy support soon to come. This means that packages from custom imported repos outside of the built-ins for a distro may be specified as dependencies in Dalec for the Build, Install, and Test phases.

The following spec fragment gives a good example of the feature:

dependencies:
  build:
    custom-repo-package:

   # NEW PROPERTY of `dependencies`
  extra_repos:
    - envs:
         # this indicates which stage a custom repo will be available for. Other options are `test` and `install`
        - "build" 
      # list repo configs to import here
      config:
        custom.repo:
          # this must be a source which contains a single file, the contents of `custom.repo`
          http:
            url: https://mypackagecenter/custom.repo
        # add other repos here...

     # list GPG public keys to import here:
     keys:
       MY-RPM-GPG-PUBLIC-KEY: 
          http:
            url: https://anotherkeysource.url/MY-RPM-GPG-PUBLIC-KEY
     
     data: 
        - dest: /opt/repo
           spec:
             context:
               # this would have to be all repo data including packages and any metadata, essentially
               # a local repo created with `createrepo`
               name: "my-custom-repo-data"
       

Note that the keys portion of the spec would not be necessary if the repo config references a key directly via http in the gpgkey field.

Which issue(s) this PR fixes (optional, using fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when the PR gets merged):
Closes #211

Special notes for your reviewer:

[cpuguy83]

Just one minor thing but otherwise this LGTM
Great work!