Can't setup with non-writable htaccess

[PVince81]

As far as I remember, some setups are configured fully read-only, or some admins don't want to let the web server write anything in the PHP tree, so they disable it.

We should allow non-writable htaccess.

This PR #32230 makes it throw an exception.

We should soften it and output a warning on the console when it happens.

@individual-it

[PVince81]

reading https://doc.owncloud.org/server/10.0/admin_manual/configuration/server/index_php_less_urls.html?highlight=htaccess#prerequisites seems to imply that having htaccess non-writable is also ok. you only need to make it writable if you want this extra thing.

[ownclouders]

GitMate.io thinks possibly related issues are #32230 (throw exception when .htaccess file is not writable), #34461 ([stable10] throw exception when .htaccess file is not writable), #18260 (Cannot setup stable8), #23207 (.htaccess RewriteRule brakes non-standard alias), and #25755 (home storage not writable).

[individual-it]

exception should not be thrown on installation or update but only on occ maintenance:update:htaccess
whoever does that clearly wants to update the htaccess file and if that fails an exception should be thrown

[individual-it]

PR here #34478