[winlogbeat] Only init metrics if needed

[marc-gr]

Proposed commit message

Add check on winlog metrics to prevent panic.

Metrics initialization was deferred to avoid registering them on CheckConfig calls. Now that is inside Open we need to check to avoid panicking when retrying on recoverable errors.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

No changelog entry since the change that introduced this is still not released.

[elasticmachine]

Pinging @elastic/sec-windows-platform (Team:Security-Windows Platform)

[intxgo]

does it mean that l.Open is called twice without l.Close? If so, there seems to be more issues

https://learn.microsoft.com/en-us/windows/win32/api/winevt/nf-winevt-evtsubscribe#return-value

so perhaps

-return l.openChannel(bookmark)
+ if l.subscription {
+    win.Close(l.subscription)
+}
+return l.openChannel(bookmark)

[marc-gr]

It only gets called more than once in case it fails to open, so no need to call close in that case.