This commit adds an API endpoint for notifying the preview server about PR
updates (`/pr-updated`). According to the update, the preview server can take
several actions. Currently, it will only check and (if necessary) update the
PR's preview visibility (but more actions could be supported in the future).
The API can be used with an automatic trigger (e.g. a GitHub webhook) to
instantly update a PR's preview visibility when it changes.
Fixes#16526
Previously, `BuildCreator#changePrVisibility()` would throw an error if the PR's
visibility was already up-to-date or if the PR directory did not exist (e.g. was
removed). This method was only used from inside `BuildCreator#create()`, which
had already checked for the existence of the directories.
This commit renames `changePrVisibility()` to `updatePrVisibility()` and makes
it more "forgiving" (i.e. it will only throw if both public and non-public
directories exist). This allows it to be used on events that may or may not have
caused the PR's visibility to change (e.g. a GitHub webhook triggered whenever a
PR's labels change).
Georgios Kalpakas