Keep downloaded agent binary until agent upgrade is completed

[juliaElastic]

Related to https://github.com/elastic/ingest-dev/issues/2878

During agent upgrade, there could be failures that cause the upgrade to be retried. When the retries happen, the agent binary should not be downloaded multiple times.
Keep the downloaded agent binary until the upgrade is completed successfully, and delete when the upgrade is completed.

[elasticmachine]

Pinging @elastic/elastic-agent (Team:Elastic-Agent)

[cmacknz]

I think this may fall out of the rollback implementation which should introduce a TTL for old agent versions. I don't think we should work on this until that RFC is completed so we can see where it fits in. Moving to blocked.

• [Elastic Agent] Allow the binary upgrade action to also rollback the agent version to the previous working version/state kibana#172745

[nimarezainia]

moving this out of sprint40 for now.

[nimarezainia]

@pchila @cmacknz do we need this issue open? will it be addressed already with the current rollback implementation?

[cmacknz]

Yes, this is suggesting that we keep the new agent version on disk util we complete the upgrade. The rollback is keeping the previous version of the agent until a TTL expires.

[ebeahan]

I don't think we should work on this until that RFC is completed so we can see where it fits in. Moving to blocked.

Do we still consider this blocked by any other work?

[cmacknz]

We should wait until the upgrade rollback implementation is complete with its current feature set before looking at this one.