#12991051 Site Profiler: Add initial version of Basic metrics

Related to Automattic/dotcom-forge#6674

Proposed Changes

• Add the initial version of the Basic Performance Metrics
• Calls the new site-profiler/metrics/basic endpoint and populate the data
• Adds the feature flag site-profiler/metrics that will be enabled in dev, wpcalypso and horizon
• Adds a dictionary with the units of the metrics
• Adds a debug statement to notify about errors, to enable it run localStorage.debug = 'apps:site-profiler' in the developer console

Testing Instructions

• Apply this patch to your environment and run Calypso locally
• Navigate to the /site-profiler URL and enter a site, e.g. example.com
• Check that the Basic Performance Metrics section is displayed with data about the Crux API metrics

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• https://wpcalypso.wordpress.com/devdocs/docs/testing/index.md for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?