Document maximum memory allocation in job options

Problem

The maximum amount of memory that can be allocated through job options is not documented and varies by backend instance:

Currently, users only discover the limit when they exceed it and receive an error like:

OpenEoApiError: [400] Internal: Requested too much executor memory: 8G + 500m, the max for this instance is: 24G (ref: r-2602131154304261886cfd5934217136)

Proposed Solution

The maximum memory limit should be exposed and documented in the processing_parameters endpoint.

Example: https://openeo.dataspace.copernicus.eu/openeo/1.2/processing_parameters

This would allow users to:

1. Discover the limit programmatically before submitting jobs
2. Understand the constraints of their backend instance
3. Adjust their job options accordingly

Additional Context

The backend already validates and reports the limit in error messages, so the information is available - it just needs to be exposed through the API in a standardized way.

Start by inspecting the processing_parameters endpoint, using the linked openEO example, and trace where the backend validates executor memory and produces the reported limit. Done means the backend-specific maximum is exposed through the endpoint in a standardized, programmatically discoverable form and is documented for users.