Add an authentication cache for API keys

[jaymode]

This commit adds an authentication cache for API keys that caches the
hash of an API key with a faster hash. This will enable better
performance when API keys are used for bulk or heavy searching.

[elasticmachine]

Pinging @elastic/es-security

[bizybot]

ERROR   1.12s J6 | RemoveCorruptedShardDataCommandIT.testCorruptIndex <<< FAILURES!
15:33:02    > Throwable #1: ElasticsearchException[Shard does not seem to be corrupted at /var/lib/jenkins/workspace/elastic+elasticsearch+pull-request-1/server/build/testrun/integTest/J6/temp/org.elasticsearch.index.shard.RemoveCorruptedShardDataCommandIT_6CA12188F8442DE5-001/tempDir-002/data/nodes/0/indices/kqxJ4VPJRX66Ecry7ezPbg/0]
15:33:02    > 	at org.elasticsearch.index.shard.RemoveCorruptedShardDataCommand.lambda$execute$1(RemoveCorruptedShardDataCommand.java:367)
15:33:02    > 	at org.elasticsearch.index.shard.RemoveCorruptedShardDataCommand.findAndProcessShardPath(RemoveCorruptedShardDataCommand.java:211)
15:33:02    > 	at org.elasticsearch.index.shard.RemoveCorruptedShardDataCommand.execute(RemoveCorruptedShardDataCommand.java:297)
15:33:02    > 	at org.elasticsearch.index.shard.RemoveCorruptedShardDataCommandIT$2.onNodeStopped(RemoveCorruptedShardDataCommandIT.java:192)
....
15:37:14 > Task :server:integTest FAILED
15:37:14 Tests with failures:
15:37:14   - org.elasticsearch.index.shard.RemoveCorruptedShardDataCommandIT.testCorruptIndex

I think the fix for #36189 needs to be backported, but not sure as the PR related to it talks about zen2 which I assume is not backported to 6.x. I will check with Armin.

@elasticmachine run elasticsearch-ci/1