Provide an alternative processing for the erratas that are created by us

[javihernandez]

Right now, the errata workflow is designed to always process erratas coming from external sources. As we are now going to create our own security advisories, we need to adjust our workflow a bit in order to fully support the feature. The only thing that makes our erratas specials is that we don't need to match the errata packages, as we are already providing it when creating the errata. We need to:

• Add a flag in the errata creation schema that we can use to identity those through the workflow (creation and release)
• Skip errata packages mapping and create errata_to_albs_packages alongside errata packages upon creation

We might also consider adding the flag above in our data model, something like "source", where possible values could be ["Red Hat", "AlmaLinux"]. This way, other sources such as "Oracle" can be added afterwards in case we decide to get it into the mix.

[javihernandez]

Even though we'll need to do something about this in the future, the core team thinks that for now it's fine as we won't be creating a lot of erratas on our own and we can anytime reset the package mappings. Feel free to reopen if needed.

[javihernandez]

After more discussions related to #415, we think that we should definitely add an alternative processing for errata packages in advisories created by us.