For DBless mode we need to have the schema documented.

### Where is the problem?

https://docs.konghq.com/gateway/2.8.x/reference/db-less-and-declarative-config/

### What happened?

There is no documented reference for the schema definition for Kong GW for either version 1.1 (as recognised by decK) or the version 2.1 (as recognised by Kong when used to do an initial setup of the Kong Gateway in DBLess mode.).

This leads to confusion when trying to create tooling to assist with setup and maintenance.

### What did you expect to happen?

We should be able to see a reference for the 1.1 schema definition
We should be able to see a reference for the 2.1 schema defnition
We should have a change list, detailing the changes between these.

### Code of Conduct and Community Expectations

- [X] I agree to follow this project's Code of Conduct
- [X] I agree to abide by the Community Expectations

Start with the linked DB-less and declarative configuration documentation and compare the schema definitions recognized by decK (1.1) and Kong Gateway (2.1). Document references for both versions and include a changelist describing their differences; confirm the work belongs in the successor documentation repository because this repository is archived.

Written by the indexing model from the issue text.