Add new Search API processor plugin for more generic data indexing

Drive-by comment: We implemented a custom processor that skips entities that have noindex set on metatags, because in pretty much all cases that we've seen, content that isn't indexed publicly should also not be indexed in your internal search, things like thank you pages and so on.

Probably doesn't really fit in this issue but I could look into creating an issue with our code if there's interested for that.

That's an interesting idea, it kinda skips the need for search_api_exclude → by using the checkbox from Metatag.

I'd be happy to include that, if you'd be willing to throw it into a new issue. Thank you!

Thanks for the patch, it's working nicely. I did find an issue with the "all metatags including defaults" option, it looks like the config value isn't being read. Attached a patch and interdiff.

The last submitted patch, 25: metatag-n3315049-24.patch, failed testing. View results →
- codesniffer_fixes.patch Interdiff of automated coding standards fixes only.

A big thank you to everyone who's contributed to this issue! I (perhaps foolishly) upgraded directly from v1.22 to v2.0.0 and ran into a *lot* of search-api-integration issues with metatag fields, and this issue seemed to be the most current one to help me get back on track.

I'm not sure if this is still the right place to follow for official post-v2.0.0 search-api integration? Issue #3326104 seems to suggest that this current issue will be used to re-implement search-api integration in 2.x, but the recent patches and activity in this issue seem to be focused on the 1.x branch, and consequently the patches don't work as-is with the 2.x branch code. But perhaps that will be coming with future activity?

Regardless, for what it's worth I adapted the most recent patch from @benabird (metatag-n3315049-24.patch) to work with the 2.x branch. It seems to work as intended in a Drupal 9.5.10 (PHP 8.1.x) environment, but I suspect it has the same test failures that the #24 and previous patches triggered.

Ran into a similar situation as above, with a site that was previously using the old patches. Need to upgrade that site to the "new" metatags/Search API methodology eventually, but not today haha.

I re-rolled this patch for Metatag 2.0.2 support, since #28 doesn't apply anymore.
I did not include the README edits, since this approach shouldn't be supported anymore anyhow.

@nuuou what is the 'new methodology' you mention ? how do we achieve this without the patch ?

Y'know, I think was wrong about the "new methodology". There are quite a few related issues to this, I thought this was solved in a different way!

Looks like this is the issue to follow going forward on this. [#3326104]

Lemme re-roll that patch again with the README.
Also, tagging this to 2.x since that's the recommended version now.

Created an MR based on the above, against 2.0.x.
Patch file created for folks who want that for Composer patches too.

Thanks @nuuou, the merge request worked perfectly for my use case. I was trying to index keywords, and this patch made it work nicely : )