Website: add documentation for zkApps

[dannywillems]

No description provided.

[github-actions]

⚠️ Code Reference Verification Failed

The documentation contains code references that do not match the current state of the codebase on the develop branch.

Issues Found

• website/docs/developers/zkapps.md:43 - Code reference to ledger/src/scan_state/transaction_logic.rs#L3588-L3592 differs from GitHub (develop branch). The referenced code may have been modified locally but not yet merged to develop.
• website/docs/developers/zkapps.md:68 - Code reference to ledger/src/scan_state/transaction_logic.rs#L2758-L2761 differs from GitHub (develop branch). The referenced code may have been modified locally but not yet merged to develop.
• website/docs/developers/zkapps.md:80 - Code reference to ledger/src/scan_state/transaction_logic.rs#L2645-L2659 differs from GitHub (develop branch). The referenced code may have been modified locally but not yet merged to develop.
• website/docs/developers/zkapps.md:160 - Code reference to ledger/src/scan_state/transaction_logic.rs#L3668-L3684 differs from GitHub (develop branch). The referenced code may have been modified locally but not yet merged to develop.
• website/docs/developers/zkapps.md:211 - Code reference to ledger/src/scan_state/transaction_logic.rs#L59-L154 differs from GitHub (develop branch). The referenced code may have been modified locally but not yet merged to develop.
• website/docs/developers/documentation-guidelines.md:38 - Code reference to ledger/src/scan_state/transaction_logic.rs#L3588-L3592 differs from GitHub (develop branch). The referenced code may have been modified locally but not yet merged to develop.

Action Required

The code referenced in the documentation must be merged to develop before documentation can be added/modified.

Please follow this workflow:

1. Merge the code changes to develop first (this PR or a separate code PR)
2. Create a follow-up PR with the documentation updates that reference the merged code
3. The verification will pass once the code is available on develop

See the documentation guidelines for more information about the two-PR workflow.