Set STATE_INITIALISING before loading config #68

[bwalkerl]

Resolves #68

The root cause of this issue is essentially:

• Forcedcache initialises stores to test if the forced cache will work https://github.com/catalyst/moodle-tool_forcedcache/blob/MOODLE_405_STABLE/classes/cache_config.php#L239
• MDL-80815 added di::get(clock::class) to the initialisation of redis cache (main only)
• Calling that initialises di, which initialises hookcallbacks, which make use of caching
• When trying to create the definition it fails $instance->get_definition_by_id once which has debugging output we see
• Debugging output this early breaks session_set_save_handler(), which is fatal if you don't have an existing session.

The solution appears to be setting STATE_INITIALISING to use ad-hoc cache for that request.

This is done in the core cache factory and should be relatively safe as $this->updating_finished() will set it to STATE_READY when finished. It was originally removed as part of #11 so we might want to double check the mentioned edge caches.