Handle redirected servers in server detection.

[annando]

This handles a problem with services like brid.gy, where urls like bsky.brid.gy are a redirect to fed.brid.gy. This formerly lead to the problem that posts from that host hadn't been displayed with the correct icon.

See snarfed/bridgy-fed#1769

[AlfredSK]

I get an error when running postupdate manually.

sudo -u www-data php bin/console.php postupdate
Check for pending update actions.
ALTER IGNORE TABLE `gserver` DROP INDEX `redirect-gsid`; 

Error 1553 occurred during database update:
Cannot drop index 'redirect-gsid': needed in a foreign key constraint
Done.

[annando]

@AlfredSK see #14823