chore(cat-gateway): Remove POST /v1/document and related components

[apskhem]

Description

• Removed POST /v1/document endpoint entirely
• Removed related integration test to the endpoint
• Removed Full signed document query in the event-db as it's no longer used

Related Issue(s)

Closes #3199

Please confirm the following checks

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream module

[damian-molinski]

Don't merge it until we're all ready for it please