fix(startup): improve startup detection for bucket creation (backport #23)

[mergify]

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Related to cryostatio/cryostat-helm#115
See #4

Description of the change:

Changes a bit of logic in the entrypoint script for detecting if the SeaweedFS storage "cluster" is ready. The previous method relied on a "cluster.check" command with a relatively long timeout, but the startup would sometimes take longer than this timeout. In these slow startup cases, the entrypoint's forked process would continue to try to create the specified S3 buckets, even if the cluster was not yet ready. The bucket creation would fail, leaving the storage in an "uninitialized" state - Cryostat would not find its expected buckets in this storage instance later on. This change sets a shorter timeout on the "cluster.check" command and loops on it, as well as increases a few sleep durations, to try to ensure that the cluster is really ready before the forked process tries to initialize the buckets.

Motivation for the change:

How to manually test:

1. Check out feat(deployment): split out -db and -storage deployments cryostat-helm#184
2. Check out this PR and build it, or use quay.io/andrewazores/cryostat-storage:startup-check-1
3. Get a Kubernetes or OpenShift cluster
4. Using OpenShift (crc) as an example, $ helm install cryostat --set authentication.openshift.enabled=true --set core.route.enabled=true --set pvc.enabled=true --set storage.image.repository=quay.io/andrewazores/cryostat-storage --set storage.image.tag=startup-check-1 ./charts/cryostat/
5. Open Cryostat Web UI and ensure that Archives view is available, and other archive-related operations work

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   This is an automatic backport of pull request fix(startup): improve startup detection for bucket creation #23 done by Mergify.