Use authenticated requests to fetch files from Phabricator revisions

[suhaibmujahid]

Here we fetch the file without going through the Conduit API:

bugbug/bugbug/tools/core/platforms/phabricator.py

Lines 312 to 318 in c600ea0

	client = get_http_client()
	r = await client.get(
	f"{_base_url()}/differential/changeset/?view={view}&ref={changeset_id}",
	)
	r.raise_for_status()
	return r.text

This limits the ability to fetch changes from restricted revisions, even if they are not security related. Using a Conduit API for that would be a better path. However, we do not have that API yet, so we need to implement it in Phabricator first.

[nordzilla]

I would love to have this functionality.