clean_blog_cache needs a hook

[spacedmonkey]

Unlike other cache clear functions, clean_blog_cache doesn't have a hook.

[spacedmonkey]

I have named it the hook clean_site_cache. I know the function is called clean_blog_cache, but want to keep inline with multisite naming.

[jeremyfelt]

Replying to spacedmonkey:

I have named it the hook clean_site_cache. I know the function is called clean_blog_cache, but want to keep inline with multisite naming.

I think that's the right call. We don't have a clean_site_cache() to confuse with and we would likely introduce a clean_network_cache() instead if it was ever needed.

[jeremyfelt]

In 37204:

Multisite: Fire a clean_site_cache action when a site's cache is cleared

Props spacedmonkey.
Fixes #36203.