feat: add support for `server_definitions` RPC

[mvadari]

High Level Overview of Change

Title says it all.

Context of Change

https://github.com/XRPLF/rippled/pull/4703

Type of Change

• [x] New feature (non-breaking change which adds functionality)
• [x] Tests (You added tests for code that already exists, or your new feature included in this PR)

Did you update HISTORY.md?

• [x] Yes

Test Plan

Added tests. Pass in CI.