Disable public gateway in incognito

[spylogsster]

Resolves brave/brave-browser#16737

• do not redirect public gateway for incognito profiles

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:

1. new profile
2. launch Brave
3. set Method to resolve IPFS resources to Gateway in brave://settings/ipfs
4. do either/both a Private Window / Guest Window
5. load ipns://brantly.eth or ipfs://QmbWqxBEKC3P8tqsKc98xmWNzrzDtRLMiMPL8wBuTGsMnR

[iefremov]

lgtm

[stephendonner]

Verified FIXED using

Brave | 1.28.64 Chromium: 92.0.4515.81 (Official Build) nightly (x86_64)
Revision | dba3af0a9a48954c8b188bc641e651580b7cb7b5-refs/branch-heads/4515@{#1162}
OS | macOS Version 11.4 (Build 20F71)

Steps:

1. new profile
2. launched Brave
3. set Method to resolve IPFS resources to Gateway in brave://settings/ipfs
4. opened the following: New Private Window, Guest Window, and New Private Window with Tor
5. loaded ipns://brantly.eth and ipfs://QmbWqxBEKC3P8tqsKc98xmWNzrzDtRLMiMPL8wBuTGsMnR

Confirmed neither of the two URL schemes loaded in any of those 3 window types

ipns://

private window	private window with tor	guest window

ipfs://

private window	private window with tor	guest window