docs: add arrivals-and-departures-for-location endpoint

[3rabiii]

Description

This PR adds the missing documentation for the arrivals-and-departures-for-location API endpoint.

Changes Included:

• New Method Page: Created arrivals-and-departures-for-location.md containing a complete list of all supported query parameters (including latSpan, routeType, emptyReturnsNotFound, etc.).
• Sample Response: Added a detailed JSON payload matching the legacy Java server output to clarify the nested entry and nearbyStopIds structure.
• Navigation: Registered the endpoint in rest_api.json so it appears in the side navigation menu.
• Element Link: Added a reference to this new endpoint in arrival-and-departure.md since it returns this element as part of its payload.

Local Preview (Screenshots)

Here is how the new endpoint and the updated elements page look like when running locally:

@aaronbrethorst
closes: #165