Add options for excluding archives and forks

[jwodder]

Possible levels at which this could be configured:

• Add archives = BOOL and forks = BOOL fields (default values True) under [reponews.repos] for including/excluding all archives and/or forks

• Support specifying archives and forks on a per-owner level, possibly via something like:

  [reponews.repos]
  include = [
      # Like "some-user/*", but with options:
      { owner = "some-user", archives = BOOL, forks = BOOL }
      # Setting one or both options to `true` overrides a corresponding `false` setting
      # for `reponews.repos.{archives,forks}`
  ]

• Support applying archive & fork filters to just affiliated repositories somehow

  • Add archives = BOOL and forks = BOOL fields under [reponews.activity.affiliated]?
  • I don't think there's an efficient way to check which affiliation an affiliated repository has, so per-affiliation filters aren't an option
  • What should happen if a given archive or fork repository is included via both affiliation and inclusion but the corresponding filters disagree?