[DOC] Upgrade for each dependency is hard to maintain

[marcalff]

In light of #2676 and #2677, it turns out upgrading each dependency is not trivial, because versions numbers for each dependencies are spread in multiple files in the source code, some of them long forgotten and easy to overlook.

In this case, opentelemetry-proto was updated to 1.3.1 in a few places, but left as 1.1.0 in others.

Provide maintainers documentation that lists exhaustively, for each dependency:

• where the dependency comes from
• what are the minimal version requirements
• which files needs to be updated
• which special build or tests need to be considered
• anything else relevant for maintainers