Switch remote settings URL to new GCP-specific endpoint on stage & prod (#21204)

* Revert "Revert "Update Remote Settings URLs after GCP migration (#20642)" (#20729)"

This reverts commit 257b6283c0.

* Add support for REMOTE_SETTINGS_WRITER_URL env variable (defaulting to GCP URL if absent)

src/olympia/conf/prod/settings.py

@@ -68,7 +68,9 @@ EXTENSION_WORKSHOP_URL = env(
 )
 
 REMOTE_SETTINGS_API_URL = 'https://firefox.settings.services.mozilla.com/v1/'
-REMOTE_SETTINGS_WRITER_URL = 'https://settings-writer.prod.mozaws.net/v1/'
+REMOTE_SETTINGS_WRITER_URL = env(
+    'REMOTE_SETTINGS_WRITER_URL', default='https://remote-settings.mozilla.org/v1/'
+)
 REMOTE_SETTINGS_WRITER_BUCKET = 'staging'
 
 # See: https://bugzilla.mozilla.org/show_bug.cgi?id=1633746

src/olympia/conf/stage/settings.py

@@ -74,5 +74,7 @@ EXTENSION_WORKSHOP_URL = env(
 )
 
 REMOTE_SETTINGS_API_URL = 'https://firefox.settings.services.allizom.org/v1/'
-REMOTE_SETTINGS_WRITER_URL = 'https://settings-writer.stage.mozaws.net/v1/'
+REMOTE_SETTINGS_WRITER_URL = env(
+    'REMOTE_SETTINGS_WRITER_URL', default='https://remote-settings.allizom.org/v1/'
+)
 REMOTE_SETTINGS_WRITER_BUCKET = 'staging'