UX: Network Menu: Disable testnet toggle when on testnet

[darkwing]

Explanation

At present the "Disable / Enable" Test Networks toggle is always enabled. If a user is currently on a test network, however, it's best to leave that toggle on so that the user doesn't find themselves in a spot where the current network is hidden via the toggle

Fixes: https://github.com/MetaMask/MetaMask-planning/issues/659

Screenshots/Screencaps

Manual Testing Steps

1. Open the Network Picker
2. Choose the Goerli network, watch network switch
3. Open the Network Picker again
4. See that the toggle is disabled

Pre-merge author checklist

• I've clearly explained:
  • What problem this PR is solving
  • How this problem was solved
  • How reviewers can test my changes
• Sufficient automated test coverage has been added

Pre-merge reviewer checklist

• Manual testing (e.g. pull and build branch, run in browser, test code being changed)
• PR is linked to the appropriate GitHub issue
• IF this PR fixes a bug in the release milestone, add this PR to the release milestone

If further QA is required (e.g. new feature, complex testing steps, large refactor), add the Extension QA Board label.

In this case, a QA Engineer approval will be be required.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[NidhiKJha]

LGTM

[metamaskbot]

Builds ready [091aef4]

• builds: chrome, firefox
• builds (beta): chrome
• builds (flask): chrome, firefox
• build viz: Build System
• mv3: Background Module Init Stats
• mv3: UI Init Stats
• mv3: Module Load Stats
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• code coverage: Report
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5
  • common: 0, 1, 2, 3, 4, 5
  • content-script: 0
  • contentscript: contentscript
  • disable-console: disable-console
  • inpage: inpage
  • policy-load: policy-load
  • sentry-install: sentry-install
  • ui: 0, 1, 10, 11, 12, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (1548 ± 33 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	105	167	125	15	7
		domContentLoaded	1414	1673	1548	69	33
		load	1414	1673	1548	69	33
		domInteractive	1414	1673	1548	69	33

Bundle size diffs

• background: 0 bytes
• ui: 42 bytes
• common: 0 bytes

[NidhiKJha]

@darkwing I think this PR fixes this issue as well

Screen.Recording.2023-07-14.at.4.33.03.PM.mov

[metamaskbot]

Builds ready [34fc16b]

• builds: chrome, firefox
• builds (beta): chrome
• builds (flask): chrome, firefox
• build viz: Build System
• mv3: Background Module Init Stats
• mv3: UI Init Stats
• mv3: Module Load Stats
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• code coverage: Report
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5
  • common: 0, 1, 2, 3, 4, 5
  • content-script: 0
  • contentscript: contentscript
  • disable-console: disable-console
  • inpage: inpage
  • policy-load: policy-load
  • sentry-install: sentry-install
  • ui: 0, 1, 10, 11, 12, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (2098 ± 95 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	130	251	194	34	16
		domContentLoaded	1739	2483	2095	195	94
		load	1739	2483	2098	197	95
		domInteractive	1739	2483	2095	195	94

Bundle size diffs

• background: 0 bytes
• ui: 3 bytes
• common: 0 bytes