Require/enforce "main" or "permalink" algorithm references

[soxofaan]

Observation from reviewing https://github.com/ESA-APEx/apex_algorithms/pull/44: some references use feature branch references: e.g.

• algorithm_catalog/eurac_pv_farm_detection.json refers to https://raw.githubusercontent.com/ESA-APEx/apex_algorithms/refs/heads/hv_pv_detection/openeo_udp/eurac_pv_farm_detection/eurac_pv_farm_detection.json
• benchmark_scenarios/eurac_pv_farm_detection.json refers to https://raw.githubusercontent.com/ESA-APEx/apex_algorithms/refs/heads/hv_pv_detection/openeo_udp/eurac_pv_farm_detection/eurac_pv_farm_detection.json

note that both of these contain refs/heads/hv_pv_detection which means that they track the feature branch hv_pv_detection of the PR itself. These references will break once the hv_pv_detection feature branch is removed.

Can/should we enforce pinned references (called "permalink" in the github UI) and/or main branch references? This could be handled as pre-commit things and in unit tests

[HansVRP]

It is also somewhat inconvenient for entry users to retrieve such a link. For future versions it could be useful to explore how this could be facilitated to automated.