[Fleet] Retry 502 errors from Elastic Package Registry

[joshdover]

Kibana version: 8.2, main

Fleet's setup procedure can fail if we receive a transient 502 error from the registry. We should gracefully retry this type of error with some exponential backoff logic up to a max number of retries before failing all of the setup procedure. This can result in an error like:

Kibana Fleet setup failed: http POST request to https://kibana-zbjc-kb-http.e2e-hqiu1-mercury.svc:5601/api/fleet/setup fails: [Elastic Agent on ECK policy] could not be added. [system] could not be installed due to error: [PackageNotFoundError: [system] package not found in registry]: <nil>. Response: {"statusCode":500,"error":"Internal Server Error","message":"[Elastic Agent on ECK policy] could not be added. [system] could not be installed due to error: [PackageNotFoundError: [system] package not found in registry]"}

Currently we rely on either Fleet Server to retry calling setup (which is not always configured to do so) or the user visiting the Fleet UI.

This should only affect instances where the only preconfigured packages are not all bundled packages. In the case of Cloud, all packages we preconfigure there are bundled.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[kpollich]

This seems like it might be related to or the same issue as #129696