Add analyzer.rb to get some statistics on an errata JSON

[m-bucher]

Take those values with a grain of salt fro the following reasons:
Packages per Erratum counts all releases, so if an erratum fixes problems in multiple releases, this multiples the number of packages. E.g. DSA-5737-1 fixes libreoffice in bookworm and bullseye, which each have ~300 libreoffice packages => 626 packages in total.

$ bundle exec ruby analyzer.rb debian_errata.json 
Errata: 3349
Releases average per Erratum: 1.14
Packages:
  average per Erratum: 35.18
  max per Erratum: 626 (DSA-5737-1)
  min per Erratum: 1

[maximiliankolb]

@m-bucher Please have a look at the linting issues to fix GHA & make rubocop happy. Looks like all of them are correctable: See https://github.com/ATIX-AG/errata_parser/actions/runs/11408114015/job/31745604046?pr=14#step:7:43

GHA is green

[maximiliankolb]

Thank you Markus for fixing linting with Rubocop.

@sbernhard Does your ACK still stand?