Update Brave Talk Links

[bsclifton]

Fixes brave/brave-browser#17146
Fixes brave/brave-browser#17147

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
• 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, npm run lint, 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:

[bsclifton]

Ready for review 😄
cc: @stephendonner @simonhong

[stephendonner]

Yes please and thanks!

[simonhong]

👍🏼

[stephendonner]

Verified PASSED using

Brave	1.29.38 Chromium: 92.0.4515.115 (Official Build) nightly (x86_64)
Revision	48cb2f4029b84b003719740a6cf9ca73f374a857-refs/branch-heads/4515_105@{#4}
OS	macOS Version 11.5.1 (Build 20G80)

For brave/brave-browser#17147:

Steps:

1. new profile
2. launched Brave
3. opened a new-tab page
4. on the bottom right, clicked on the Try it out button

Confirmed the link is now to https://talk.brave.com/widget

For brave/brave-browser#17146

Steps:

1. new profile
2. launch Brave
3. load a new-tab page
4. click on Edit cards
5. add the Brave Together (to be renamed to Brave Talk) card
6. open the Network panel in Developer Tools
7. click on the Start video call button
8. look at the URLs/redirects

Confirmed the URL is now https://talk.brave.com/widget