[extension/opampextension]: Adding AcceptsRestartCommand capability

[bvigar]

Description

This changes implements the OpAMP AcceptsRestartCommand capability for the extension. This functionality exists in the OpAMP supervisor already, and works by rebooting the collector with the new config file. For this change, the implementation sends the SIGHUP signal to the collector to initiate a safe restart.

The intention of adding this functionality is to support reloading updated config in the collector via file or http config provider instead of trying to reload config in memory and potentially rebuild the component graph and swap it out at runtime.

Link to tracking issue

Fixes

Testing

• Added unit test for the changes to onCommand in the OpAMP agent to validate the SIGHUP is sent
• I haven't done any e2e testing locally yet, I plan to in the next few days

Documentation

• Updated the extension/opampextension/README.md to show the support for the new capability

[bvigar]

It was discussed sending SIGUSR2 instead of SIGHUP here, but I noticed the collector doesn't currently handle the SIGUSR2 yet the way it currently handles SIGHUP, so that functionality can be added in a future iteration

[bvigar]

After talking some more with @evan-bradley , i'm going to switch to implementing this under the AgentCapabilities_AcceptsRestartCommand capability instead. I'm also going to add a feature gate to put this behind, so standby. I'll move this to draft in the meantime.

[atoulme]

Please take a look at the build, fix the CI and mark ready for review again.

[evan-bradley]

Thanks for working on this @bvigar.

[douglascamata]

@bvigar the PR title mentions AtteptsRemoteConfig capability, but the PR itself is implementing AcceptsRestartCommand. Could you update the title please to avoid confusion?

[evan-bradley]

Looks good to me, sorry for the long review cycle.

[otelbot]

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