Collect the set cache events and size of the cached objects

Closes #3437625

added 4 commits

• f3c1a824...c3ea9c4a - 3 commits from branch project:2.x
• cfe058ee - Merge branch '2.x' into '3437625-collect-the-set-cache-events'

Compare with previous version

I'm undecided on this. I think we should skip the logging of size during get(). Its too costly to run serialize() again. I'd be OK with it if we could somehow leverage the serialize that the cache backend is already doing.