Make muting sites easier

[fallaciousreasoning]

Resolves brave/brave-browser#6690

This a couple of things to make muting a bit more customizable:

• Adds an option to brave://settings/system for toggling whether or not the mute indicators on tabs are clickable
  
• Adds a new (Un)Mute tab entry to the context menu which mutes/unmutes only the tab (or selected tabs) rather than the origins (or selected origins).
  

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run lint, npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

1. Open Brave
2. Mute indicators should be clickable
3. In brave://settings/appearance, enable Disable mute function in tab speaker icons
4. Mute indicators should not be clickable
5. Right click on a tab and you should see a new Mute tab entry.
6. It should be above the existing Mute site entry.
7. It should be possible to Mute/unmute tabs.
8. It should override the Mute/unmute sites option.

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[sangwoo108]

LGTM but I think you might want to wait for @simonhong 's review :)

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[simonhong]

++ 👍🏼

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[mkarolin]

chromium_src LGTM (with 1 nit)

[brave-builds]

A Storybook has been deployed to preview UI for the latest push