Use the MedusaConfiguration API when creating Medusa configuration

[rzvoncek]

What this PR does:

• Adds an ObjectReference to the Medusa spec to allow referencing MedusaConfig.
• Modifies the k8ssandra cluster creation webohook to error out if the reference is present but the medusa storage prefix is not set in the cluster's spec.
• When creating the cluster, or rather it's medusa.ini config map, merge both the MedusaConfig and the cluster spec, giving priority to the later.

Which issue(s) this PR fixes:
Fixes #1158.

Checklist

• Changes manually tested
• Automated Tests added/updated
• Documentation added/updated
• CHANGELOG.md updated (not required for documentation PRs)
• CLA Signed: DataStax CLA

[codecov]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (651e3f7) 57.13% compared to head (f25a17c) 57.15%.

❗ Current head f25a17c differs from pull request most recent head f3a2bed. Consider uploading reports for the commit f3a2bed to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1187      +/-   ##
==========================================
+ Coverage   57.13%   57.15%   +0.01%     
==========================================
  Files         103      103              
  Lines       10618    10647      +29     
==========================================
+ Hits         6067     6085      +18     
- Misses       4023     4029       +6     
- Partials      528      533       +5     

Files	Coverage Δ
...pis/k8ssandra/v1alpha1/k8ssandracluster_webhook.go	71.27% <100.00%> (+1.61%)	⬆️
controllers/k8ssandra/medusa_reconciler.go	63.92% <44.00%> (-3.99%)	⬇️

... and 3 files with indirect coverage changes

[adejanovski]

A few minor changes and a todo:

We need an e2e test for this.
Modify the single-dc-encryption-medusa fixture to add a MedusaConfiguration object and modify the K8ssandraCluster storage properties to replace them with the medusaConfigurationRef.
The medusa-bucket-key will be created already (it's at the root of the fixtures directory) so you just need to reference it in the MedusaConfiguration object.

[sonarqubecloud]

Quality Gate passed

The SonarCloud Quality Gate passed, but some issues were introduced.

2 New issues
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud