WIP: Add admin search for info requests

[laurentS]

Relevant issue(s)

#8814

What does this do?

This PR marks InfoRequest as searchable with the new search engine.

Why was this needed?

Implementation notes

This is mostly adapted from the previous PR for PublicBody.
I took the opportunity to optimise the view a bit as well. For a full page of requests, the rendering time is divided by 2-4 locally, and number of requests to db drop from ~416 to ~20.

This is probably one of the models where initial indexing time is going to matter a bit, at least for WDTK. If it runs at roughly the same speed as my local test, you're looking at ~6.5h of indexing time. I will try to implement a more generic version of the reindex_all I wrote in https://github.com/mysociety/alaveteli/pull/9415/changes, which can be used by the various models that don't need any ruby attributes in their SearchDocuments.

Screenshots

Notes to reviewer

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[laurentS]

Added another commit to do a much faster reindex_all. For my test dataset, 53k requests, it reindexes the entire set in 1.5 seconds, VS 3min 5 sec with the default reindex_all. So you should get a full reindex in under a minute for WDTK, assuming similar hardware.

The method is generic enough to also take care of MailServerLog and any model that only indexes SQL constructs.