feat: add xp-clifford submodule with sidebar and config integration

[gergely-szabo-sap]

Add xp-clifford as a git submodule under docs/ and integrate it into the Docusaurus site:

• Register submodule pointing to SAP/xp-clifford.git
• Add exclude rules in docusaurus.config.js to filter out non-docs content (subdirectories, CONTRIBUTING.md, DEVELOPMENT.md)
• Add xp-clifford entry to the navbar dropdown menu
• Add collapsed sidebar category with autogenerated items in sidebars.js

[jn-av]

Hi @gergely-szabo-sap,

Thanks for adding clifford. The README is getting really long and has a lot of information that might not be needed for a the docs.

What do you think, does it make sense to split the docs and put them into a /docs/ folder? I think the documentation could benefit from that.

I'm also looking to migrate the docs for BTP and HANA to this format:

• docs/end-user-guides: Hosting all end-user relevant information/docs.
• docs/contribution-notes: Hosting all contribution-related work (ADRs, setup info if needed, special dev decisions, and more).

Do you think this structure would also make sense for clifford, or not so much?

[gergely-szabo-sap]

Hi @jn-av,

Thanks for the great suggestion! I agree that restructuring the docs into a dedicated /docs/ folder makes a lot of sense. I'll adopt the structure you described (end-user-guides and contribution-notes) in the xp-clifford repository.

I'll make the changes there and update this PR accordingly once the submodule is ready.

[gergely-szabo-sap]

@jn-av, I updated the xp-clifford repo here: SAP/xp-clifford#46 and applied the changes to the current repo.

[jn-av]

Thanks a lot for adding the documentation. Just one thing with the submodule url, and I saw that we do not specify the order of the content in the sidebar. Can we add that?
Should be possible to add by adding this to the beginning of the files in the xp-clifford repo:

---
sidebar_position: 0
---

as seen here: https://github.com/SAP/crossplane-provider-btp/blob/main/docs/end-user-guides/account/subaccount.mdx?plain=1

[jn-av]

Could we change this to the same format as the other ones?
https://github.com/SAP/xp-clifford.git

[gergely-szabo-sap]

@jn-av, I made the requested changes.