leverage s3 conditional write for concurrent s3 metastore

[trinity-1686a]

Is your feature request related to a problem? Please describe.
today the only way to have an HA metastore is to deploy a postgres cluster (ideally setup with redundancy itself). this is a pain point, people would often prefer to use a simpler to setup S3 metastore if that provided the same level of availability

Describe the solution you'd like
provide a configuration option to allow concurrently running S3 metastores. This can be achieved by leveraging S3 conditional writes. As this is not something all alternative S3 providers supports, this should be optional, and we should, if possible, detect if the option is enabled but the provider doesn't support it (for instance, write to a random object, overwrite it with a conditional write that should fail, and verify it does indeed)

Describe alternatives you've considered
people can already use the postgres metastore, or have a non replicated metastore

[fulmicoton]

I think @fmassot would love to see this happen.

I think there are different to have this work. One possibility:
use a broken version of leader election. e.g. the metastore with the highest id is the leader.
All writes go through this "broken" notion of a leader.

Leader writes using conditional writes to ensure its write are consistent. Upon failure it reloads the model.
For searchers, upon search, if they have not written nor read the index in the last N seconds, they need to pull a up-to-date state.

TLDR:

• optimistic strategy with conditional write brings correctness
• shitty leader election brings performance

[esatterwhite]

What would be the projected performance difference?
I would assume its still possible to see occasional latency spikes, and timeouts from S3 which could cause a lot of down stream problems.

But it sounds nicer than running HA postgress