[Task]: Align available locales between addons-frontend and addons-server

[diox]

Description

addons-server splits locales into 2 lists:

• Locales available on the pages it's responsible for (devhub, etc)
• Locales that it knows about (only really exposed in statistics page AFAIK)

addons-frontend has a similar concept but does it a bit differently, and as a result the 2 aren't completely aligned.

We want to streamline locales to only offer to translate pages on AMO that we know have good completion rate, so we need to align the 2.

Acceptance Criteria

Milestones/checkpoints

Preview Give feedback

1. addons-server and addons-frontend pages offer the same locales in their dropdowns

Checks

• If I have identified that the work is specific to a repository, I have removed "repository:addons-server" or "repository:addons-frontend"

┆Issue is synchronized with this Jira Task

[diox]

Interestingly the 2 are already mostly aligned, except for languages that we need to remove or add from addons-server in #15433. So no need to do anything here.