Make add-on store base end point part of the public API (#15893)
Relates to #14974
Summary of the issue:
Add-on authors wish to have a stable API so that they can change the base URL of the add-on store.
This allows add-ons to use a mirror for the add-on store.
Description of user facing changes
None
Description of development approach
Change BASE_URL for the add-on store to be public
