config: protect global configOpts with a mutex

[mauri870]

There is a race condition in configOpts when one goroutine calls OverwriteConfigOpts while another reads the variable. This is common, as almost every method in config.C reads this global variable.

Fix the data race by using a mutex. Since this variable is mostly read, optimize it with a sync.RWMutex.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works

Related issues

• Relates to otel: fix data race with config opts in NewBeatReceiver beats#43294.

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: a900ef4

cc @mauri870

[leehinman]

Thank You