Cleanup Metrics Inventory view (Part 1)

[hbharding]

Related
Working group: https://github.com/elastic/observability-dev/issues/439
Figma file: https://www.figma.com/file/4678Pxjyf2T8BOfAbPxMJq/Cleanup-UI-Controls?node-id=169%3A5753

As part of an ongoing effort to cleanup parts of the Metrics UI, this issue reorganizes the layout of certain buttons, filters, and UI controls. This issue does not add or change any existing functionality.

Note: Please ignore the minimally styled waffle map in the screenshot. This is something we'd like to address in a separate issue.

Summary of what's changing:

Why "Part 1"?

There are some additional changes we'd like to make, namely around "Saved views" and introducing a bottom control bar that allows the user to easily switch between saved views. Because this changes existing functionality, we've decided to hold off on implementing this for now. We can tackle this in a separate issue. These "future" designs are available in the Figma file.

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)