Jetpack Protect: Replace user_token with blog_token.

[sergeymitr]

Changes proposed in this Pull Request:

• The WP.com API endpoint jetpack.protect.requestKey does not use the user ID, and can be authenticated using blog_token.

Jetpack product discussion

Part of the #16709.

Does this pull request change what data or activity we track or use?

No.

Testing instructions:

1. Go to "Jetpack Settings -> Security" and confirm that "Brute force attack protection" is disabled.
2. Delete the existing Protect key:

delete from wp_options where option_name = 'jetpack_protect_key';

3. Enable "Brute force attack protection".
4. Confirm that the key was created and saved into the database:

select * from wp_options where option_name = 'jetpack_protect_key';

Proposed changelog entry for your changes:

n/a

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

E2E results is available here (for debugging purposes): https://jetpack-e2e-dashboard.herokuapp.com/pr-16758

Scheduled Jetpack release: September 1, 2020.
Scheduled code freeze: August 25, 2020

Generated by 🚫 dangerJS against 267dec3

[leogermani]

Tested following the instructions and it worked as expected