Ability to remove the 'ElasticPress Indexing' option on Multisite

[johnbillion]

Is your enhancement related to a problem? Please describe.

On a Multisite installation, super admin users can uncheck the ElasticPress Indexing checkboxes on the Network Admin -> Sites screen. This is undesirable when we want to control this option at the network or site level.

Describe the solution you'd like

It would be great if there was a filter to disable this checkbox (and its Ajax handler) so we can prevent super admins from changing this setting for each site.

The setting itself can be enforced via the blog_option_ep_indexable filter.

[jeffpaul]

@johnbillion are you expecting to then have the ElasticPress Indexing checkbox displayed somewhere in the individual network site settings or are you expecting to programmatically control which sites are indexed and which are not?

[johnbillion]

The latter. I'd like to say "switch this off, I got this".