[ESLint]: Add ESLint license check.

[fallaciousreasoning]

Resolves brave/brave-browser#26575

Submitter Checklist:

• I have requested a security & privacy review here
• 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, 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

[fmarier]

While we haven't been doing that consistently at Brave, the correct headers now use the HTTPS URL:

 * file, You can obtain one at https://mozilla.org/MPL/2.0/.

So I'd suggest this:

1. we accept both in the check
2. we add the HTTPS URL for all of the missing headers we add

Instead of #1, we could also just upgrade the existing ones, but that's not really necessary.

[fallaciousreasoning]

@fmarier it should use https urls now, and I updated the tool to inject the year the file was added to source control. I haven't bothered rebasing onto master so there are a bunch of conflicts, as I think we're still a little way off merging it (pending security review ect).

[fallaciousreasoning]

@petemill for @brave/js-deps-reviewers
@emerick for @brave/rewards-client
@onyb for @brave/crypto-wallets-front-end
@jamesmudgett for @brave/crypto-wallets & @brave/ios

The changes to the files in rewards-client & crypto-wallets-front-end should just be updating or adding missing license headers.

Note: The build is failing for merge conflicts - I'm not going to fix them until we're ready to land this as we keep getting new ones.

[petemill]

We can probably bypass most of those owner reviews since we're not making any code changes.

[petemill]

Thanks for tackling this complex issue and writing an eslint plugin from scratch to accomplish it! Nice work. Hope the rebase isn't too bad.

[bsclifton]

Doing an admin merge - things should be good to go and there are just too many reviewer groups (as this touches a lot of files; but only licensing).