Upgrade Elastic to version 9+

[akatsoulas]

No description provided.

[smithellis]

It looks like our usage of elasticsearch-dsl is holding us back on this - it doesn't have a release candidate for 8+ yet. elastic/elasticsearch-dsl-py#1569

[smithellis]

mozilla/kitsune#6640

[smithellis]

Here is what I know.
I have two branches, one to take us from 7.17 to 8+, and one to go from 8 to 9.
Locally, these both function, returning search results as expected (if you make sure to es_init, es_reindex and start a celery worker).
In Elastic proper, in dev, after the migration of the server, results are not populated as expected. We appear to be returning the count of results properly, but not the actual content of the results. I believe that during the migration, I either selected a poor option for index handling, or something just got corrupted in the migration. To complicate things, I was unable to roll dev back at Elastic without issue, and I'm unclear if some of the choices I'm available to me carry risks. I'd like to replace dev at elastic with the content of stage at Elastic. Then I could re-do the migrations again and rule out some potential issues.