add link to source builder

[eviljeff]

Fixes: https://mozilla-hub.atlassian.net/browse/AMOENG-2115

Description

Adds link to source builder, gated by the waffle defined in #24131

Context

Pretty useless right now until the main PR is merged, and the source builder service is up and running

Testing

• Define and enable enable-source-builder waffle switch if you've not had it created via the migration in Call source builder API when source code is provided #24131
• Navigate to a review page for an add-on that has one or more versions with source code uploaded
• see link to Source Builder
• (better delete the waffle switch again if you created it manually)

Checklist

• Add #ISSUENUM at the top of your PR to an existing open issue in the mozilla/addons repository.
• Successfully verified the change locally.
• The change is covered by automated tests, or otherwise indicated why doing so is unnecessary/impossible.
• Add before and after screenshots (Only for changes that impact the UI).
• Add or update relevant docs reflecting the changes made.

[willdurand]

r+wc, thanks

[ioanarusiczki]

@eviljeff I guess updating this here is fine, because I've noticed something after enabling the switch on stage.

On dev it seems to be working just fine meaning I am redirected to https://addon-builder-61bc7e6a6897.herokuapp.com/login after I click on Source Builder url.
On stage it reopens the same page instead, you can try with https://reviewers.addons.allizom.org/en-US/reviewers/review/2252834

I see while hovering over the url that dev has herokuapp.com but stage has reviewers.addons.allizom.org instead.
addon id , version id are present (as expected)

[eviljeff]

I guess SOURCE_BUILDER_VIEWER_URL is only defined for addons-dev right now - I believe @willdurand added the env config for this?

[willdurand]

I guess SOURCE_BUILDER_VIEWER_URL is only defined for addons-dev right now - I believe @willdurand added the env config for this?

Yes, that's correct. This is only enabled on -dev, and in fact, it'd be best not to turn the source builder switch on on stage.

[ioanarusiczki]

ok, switch off on stage