Disable in-page translation in release channel

[yrliou]

Fix brave/brave-browser#4626

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests && npm run test-security) on
  • Windows
  • macOS
  • Linux
• Verified that all lint errors/warnings are resolved (npm run lint)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone
• Public documentation has been updated as necessary. 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-Protection-Mode
  • 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-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

1. Visit https://www.deutschland.de/de/topic/politik/frauenrechte-deutschland-foerdert-gleichberechtigung-weltweit
2. Translate bubble in the location bar should not be shown in release channel, but will be shown in any other channels.
3. Right click in the page to open the context menu, Translate to English (or any other default language) shouldn't be shown in release channel but will be shown in any other channels.
4. Open brave://settings/languages, open the language section, Offer to translate pages that aren't in a language you read switch should not be shown in release channel but will be shown in any other channels.

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

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.

[emerick]

LGTM, one minor nit.

[emerick]

Really really minor nitpick, but should it be called IsBraveTranslateEnabled?

[emerick]

LGTM

[yrliou]

Locally went through the test plan on mac by building both development&debug build and stable&official build, and on windows & linux by changing the value of is_release_channel.
mac&linux CI passed in https://staging.ci.brave.com/job/brave-browser-build-pr/job/disable_translate_in_release/2/flowGraphTable/, failed browser tests are known.
I will wait for Windows CI pass before merging.

[emerick]

LGTM