[proposal] modify updating beats and otel dependencies

Currently we have a GitHub action to update beats and a GitHub action to update otel dependencies.

This can create the scenario where the version of otel in beats submodule and elastic-agent is different, which may cause problems.

I propose that we update the otel dependencies in beats first, and then have one GitHub action in the elastic-agent repository that updates the beats submodule, and if the beats submodule imports a newer version of otel dependencies update those to match.

Now that I have proposed a solution, I expect [Cunningham's Law](https://meta.wikimedia.org/wiki/Cunningham%27s_Law) will quickly be applied.

Start by reading the existing GitHub Actions that update the beats submodule and OpenTelemetry dependencies. Trace how each workflow currently selects versions, then verify the proposed single workflow keeps the beats and otel dependencies aligned after an update.

Written by the indexing model from the issue text.