Refactor to optimise for Windows service manager checkin

[michalpristas]

This PR is huge but it does just few things.

It does not use elastic-agent-libs for calling ProcessWindowsControlEvents. ProcessWindowsControlEvents creates an objects that serves as an service instance and communicates with service manager. But having this in libs has an effect of running init section of whole elastic-agent-libs dependency tree before registering with a service.

It splits agent/cmd package into sub packages isolating each command. Service Manager communication is then moved outside to internal/pkg/agent/agentservice as described in first step. Having this split and service in a package deliberately named makes init section of agentservice being called sooner during initialization.

In agentservice init service we add WaitGroup when spinning up ProcessWindowsControlEvents goroutine. This blocks loading of subsequent packages and avoids possibility of starving ourselves of resources (when new goroutines are started later, subprocesses...). We cannot guarantee ordering of goroutines and that this one will be up in time. This is best effort of achieving that.
It's essential to have a package named like this because of the way how init section loading is implemented (alphabetical sorting plays a significant role)

Result of this is that we not just moved communication a way sooner to init section (normally end of init due to big dependency tree)
But also moved it before proceeding with initialization of

• composables
• azure, aws sdks,
• k8s,
• prometheus. and cockroachdb,
• >95% of otel dependencies,
• beats

This makes separation of otel into custom binary not critical for issues related to windows service manager communication timeouts.

Related #4971

[elastic-sonarqube]

Quality Gate failed

Failed conditions
13.8% Coverage on New Code (required ≥ 40%)

See analysis details on SonarQube

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: af2ab1a

Failed CI Steps

• Win2022:sudo:fleet
• arm:sudo: default

History

• 💔 Build #26004 failed e1fc526
• 💔 Build #25990 failed e9e04ac
• 💔 Build #25989 failed 0cc8cb3
• 💔 Build #25987 failed 1ef74cd
• 💔 Build #25985 failed ccc6a66

cc @michalpristas

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)