New Feature - Dedicated MegaMenu Cache

[kestraly]

Adds Dedicated Menu Cache to reduce page load down.

On a regular uncached page, the mega menu would need to load from the database, creating excess load and poor performance for page speed TTFB.

Changes add a cache to the System / Cache.

This means when Page Cache is flushed, it does not affect the mega menu cache and page TTFB.

Requires addtional changes to reneable the is active feature