Add missing Server Performance chart legend

[wojtekn]

Related to https://github.com/Automattic/dotcom-forge/issues/9965

Proposed Changes

I propose to add a missing legend for the Server Performance chart on the site's Monitoring page.

Why are these changes being made?

The legend is missing for the Server Performance line chart but is available for other charts.

Testing Instructions

1. Open Calypso locally or use a Calypso Live link
2. Navigate to the /sites page
3. Locate a Business site with enabled Hosting features
4. Open the site's card and click the Monitoring tab
5. Confirm that Server Performance chart has legend displayed

Before	After

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests 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 UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• 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)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-126128

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-126128&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-126128&env=a8c-for-agencies

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~4 bytes added 📈 [gzipped])

name             parsed_size           gzip_size
site-tools             +66 B  (+0.0%)       +2 B  (+0.0%)
site-monitoring        +66 B  (+0.0%)       +2 B  (+0.0%)
site-logs              +66 B  (+0.0%)       +2 B  (+0.0%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug add/missing-server-performance-chart-legend on your sandbox.