feat(buckets): add CRYOSTAT_BUCKETS for pre-created buckets

[andrewazores]

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Fixes: #3
Based on #1
Depends on #1

Description of the change:

Adds an environment variable CRYOSTAT_BUCKETS that defines a comma-separated list of bucket names that should be automatically created in the storage volume.

Motivation for the change:

See #1. It is useful to be able to declare the required buckets on the storage container itself, so that applications (like cryostat) that expect particular buckets to exist can simply assume that they do/will, rather than needing to implement behaviour to check and create them all the time on their own.

An alternate approach is to figure out what initialization work actually needs to be done (ie what is weed shell doing under the covers), and see if it is possible to do that work before executing the original entrypoint script and bootstrapping the system. This is probably more fragile to any underlying implementation changes by Seaweed, however.

How to manually test:

1. ./build.bash
2. Run the just-built image, ex.: podman run --rm -it -e CRYOSTAT_ACCESS_KEY=a -e CRYOSTAT_SECRET_KEY=b -e CRYOSTAT_BUCKETS=archivedrecordings -e WEED_V=4 -p 8333:8333 -p 8888:8888 cryostat-storage:latest
3. Wait some time (up to 30 seconds), then use the aws CLI and run: AWS_ACCESS_KEY_ID=a AWS_SECRET_ACCESS_KEY=b aws s3 ls --endpoint-url http://localhost:8333
4. The result should be a line like 2024-01-16 18:01:26 archivedrecordings, indicating the creation time of the one bucket specified in the CRYOSTAT_BUCKETS env var. Repeat this test with different CRYOSTAT_BUCKETS values, separated by commas, with lengths from 3 to 63 characters.