docs(oracle): add guides and examples

[tamalsaha]

Summary

• expand Oracle guides to match the detailed style used in Postgres docs

• replace brief/stub content with full step-by-step operational walkthroughs

• update Oracle concept and overview pages to accurately describe day-2 workflows and autoscaling behavior

• Updated example manifests to use latest active catalog version (21.3.0).

What Was Updated

• operation guides expanded with detailed flow and verification:
  • UpdateVersion
  • Restart
  • VolumeExpansion
  • Reconfigure
  • ReconfigureTLS
  • RotateAuth
  • HorizontalScaling
  • VerticalScaling
• monitoring guides expanded:
  • Builtin Prometheus
  • Prometheus Operator
• autoscaler guides expanded:
  • Compute autoscaling
  • Storage autoscaling
• core docs expanded:
  • quickstart
  • RBAC
  • private registry usage
  • custom RBAC usage
  • configuration via config file
• concepts updated:
  • Oracle
  • OracleVersion catalog
  • OracleOpsRequest
  • OracleAutoscaler
• overview pages updated across Oracle guide sections (including backup, ops-request, monitoring, tls, reconfigure, scaling, update-version, rotate-auth, autoscaler)

Notes

• changes are documentation-focused and intended to make Oracle docs consistent with existing KubeDB guide depth and structure
• PR remains scoped to Oracle documentation and related guide index updates

[github-actions]

Visit the preview URL for this PR (updated for commit 3ffe717):

https://kubedb-v2-hugo--pr868-pr-oracle-docs-i6vk8hog.web.app

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