improve rdbms aesthetics

[christinaausley]

Summary

Note: This isn't really a technical content change, this is largely for user digestion and aesthetics.

Polish pass across RDBMS and secondary storage documentation for clarity, visual quality, and terminology consistency.

Visual improvements

• Replaced plain link lists with <DocCardList /> on relational-db/index.md, secondary-storage/index.md, and manual/rdbms/index.md
• Converted 4 DB-specific permission SQL blocks in rdbms-schema-management.md to a tabbed interface (PostgreSQL, Oracle, MariaDB/MySQL, SQL Server)
• Converted TLS/SSL section in rdbms-troubleshooting.md to tabs- added missing SQL Server and MariaDB/MySQL TLS JDBC URL examples
• Replaced 6 verbose database subsections in rdbms-support-policy.md with a single summary table

Sidebar cleanup

• Added sidebar_label to child pages under "Relational databases" to drop the redundant "RDBMS" prefix from sidebar display: "Version support policy", "Configuration overview", "End-to-end setup guide", "Benchmark results" (page titles unchanged)

Wording and accuracy fixes

• Fixed broken line-break sentences across configuration.md and secondary-storage/index.md
• Fixed PostgreSQL permissions in operations.md: GRANT CREATE ON DATABASE to GRANT CREATE ON SCHEMA public
• Replaced all remaining "Web Modeler" references with "Camunda Hub" across rdbms.md, configuration.md, and rdbms-setup-guide.md
• Converted :::warning bullet in access-sql-liquibase-scripts.md to a callout block; renamed ## Optional to ## Additional resources
• Fixed relative path to absolute in configuration.md Helm driver section
• Removed redundant content: duplicate ## History cleanup intro, filler paragraph in secondary-storage/index.md, redundant "Key concepts" bullets in rdbms.md

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support. (add bug or support label)
• This is already available but undocumented and should be released within a week. (add available & undocumented label)
• This is on a specific schedule and the assignee will coordinate a release with the Documentation team. (create draft PR and/or add hold label)
• This is part of a scheduled alpha or minor. (add alpha or minor label)
• There is no urgency with this change (add low prio label)

PR Checklist

• The commit history of this PR is cleaned up, using {type}(scope): {description} commit message(s)

• My changes are for an upcoming minor release and are in the /docs directory.
• My changes are for an already released minor and are in a /versioned_docs directory.

• I added a DRI, team, or delegate as a reviewer for technical accuracy and grammar/style:
  • Engineering team review
  • Technical writer review via @camunda/tech-writers unless working with an embedded writer.

[github-actions]

👋 🤖 ✅ Looks like the changes were ported across versions, nice job! 🎉

You can read more about the versioning within our docs in our documentation guidelines.

[RomanJRW]

LGTM 👍

[github-actions]

🧹 Preview environment for this PR has been torn down.