Tezt/Cloud: fix opentelemetry agent

What

Make Opentelemetry Agent usable again, and put a Jaeger link to the dashboard

Why

It seems that recent versions of opentelemetry-collector changed some syntax and RPC, and the agent couldn't be started anymore. And having a link to Jaeger in the dashboard is always useful :)

How

• Fix the health_check service
• Remove the metrics, as the syntax is outadted since v0.123.0, and the service is started by default.
• Add the link to Jaeger in the dashboard

Manually testing the MR

A simple test to test it:

TEZOS_PPX_PROFILER=opentelemetry make
dune exec tezt/tests/cloud/main.exe -- DAL --localhost -v --tezt-cloud <your-arch> --website --prometheus --grafana --monitoring --open-telemetry --producers 1 --stake 1,1 --ppx-profiling --ppx-profiler-backends opentelemetry

Once the DAL nodes are producing and verifying shards, you should be able to see some traces in the Jaeger dashboard (http://localhost:8080/#monitoring -> Jaeger, or directly http://localhost:16686):

In particular, if you click on one:

It shows that the three DAL nodes are actually publishing their traces and they're visible as a single trace 🎉

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR