[Icon] Update Observability app icons

[formgeist]

Summary

Updating the app icons for Metrics (previously Infrastructure) and Logs to make them consistent with their solution logos, as it's the case with the other Observability apps (Code and APM).

• Update Metrics icon

• Update Logs icon

Checklist

• Checked in dark mode
• Checked in mobile
• Checked in IE11 and Firefox
• Props have proper autodocs
• Added documentation examples
• Added or updated jest tests
• Checked for breaking changes and labeled appropriately
• Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[formgeist]

@snide What would be the process for changing the variable name from infraApp to metricsApp due to the rename? Just update the parameter in the used places in Kibana in a single PR?

[snide]

I got ya, just feed the icons in. Is there one for logging as well? #2431

[snide]

And yes, if you want to change the name, we'll just need to change that in the Kibana PR when we merge it. I can remember that as well. We'll ignore it as a breaking change because that logo is super specific.

[formgeist]

Sounds good @snide - thanks!

[ryankeairns]

Previewed locally including the nav drawer page and everything looks good. File changes look correct, as well.

[formgeist]

@ryankeairns Thanks for doing a review. I'll merge now