Create AddOn API

[zugao]

Summary

• This PR changes API for how we add add-ons
• This PR fixes the problem with billing that the instance id of an add-on is the same as the parent service.

Context

Billing

We currently have a problem with billing as we are sending the same instance_id for service and it's add-on office(collabora). I order to fix this issue we decided to have a dedicated place for AddOns where we can easily track what addOns are available. This object will reside under spec.parameters. Once we know where the add ons objects are, we can easily track and use them across our comp-functions, including the billing. We also change the naming from collabora to office, as this is how it's defined in Odoo and it's also simpler to understand the add from the end user perspective.

Checklist

• Categorize the PR by setting a good title and adding one of the labels:
  bug, enhancement, documentation, change, breaking, dependency
  as they show up in the changelog
• Update tests.
• Link this PR to related issues.

[wejdross]

Can You explain this PR better? How is that going to help with billing? Why introducing Addons? - To generate prometheus rule based on that? Why naming addon as 'office' instead of 'collabora'?