operator: Allow reduced tenant OIDC authentication requirements

[periklis]

What this PR does / why we need it:
The present LokiStack CR kubebuilder annotations disallow using the gateway OIDC flow by only providing a clientID and issuerURL in the secret. This makes use cases like using token-refresher that forwards a valid IDToken impossible.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Documentation added
• Tests updated
• Is this an important fix or new feature? Add an entry in the CHANGELOG.md.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/upgrading/_index.md

[grafanabot]

./tools/diff_coverage.sh ../loki-main/test_results.txt test_results.txt ingester,distributor,querier,querier/queryrange,iter,storage,chunkenc,logql,loki

Change in test coverage per package. Green indicates 0 or positive change, red indicates that test coverage for a package fell.

+           ingester	0%
+        distributor	0%
+            querier	0%
- querier/queryrange	-0.1%
+               iter	0%
+            storage	0%
+           chunkenc	0%
+              logql	0%
+               loki	0.7%

[grafanabot]

./tools/diff_coverage.sh ../loki-main/test_results.txt test_results.txt ingester,distributor,querier,querier/queryrange,iter,storage,chunkenc,logql,loki

Change in test coverage per package. Green indicates 0 or positive change, red indicates that test coverage for a package fell.

-           ingester	-0.1%
+        distributor	0%
+            querier	0%
+ querier/queryrange	0%
+               iter	0%
+            storage	0%
+           chunkenc	0%
-              logql	-0.5%
+               loki	0%