Docs: Replace misleading CLA links (#9133)

[i-ron-y]

What is the purpose of this pull request? (put an "X" next to item)

[X] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)
I changed the CLA link from https://contribute.jquery.org/cla to https://cla.js.foundation/eslint/eslint in the following pages:

• https://github.com/eslint/eslint/blob/master/CONTRIBUTING.md
• https://github.com/eslint/eslint/blob/master/docs/developer-guide/contributing/README.md

The reason for this change is twofold:

1. To avoid confusion - https://cla.js.foundation/eslint/eslint is the actual page where ESLint contributors can sign the CLA, not https://contribute.jquery.org/cla
2. To keep them consistent with the Pull Request Guidelines page which links to https://cla.js.foundation/eslint/eslint

Is there anything you'd like reviewers to focus on?
N/A

[eslintbot]

LGTM

[platinumazure]

LGTM, thanks for contributing!