fix(github): fix octokit warnings

[LuisUrrutia]

Short description of what this resolves:

Octokit deprecation warnings

Changes proposed in this pull request:

• headers is deprecated and we shouldn't use it.
• rejectUnauthorized set to false is a security issue, and we shouldn't bother to find a workaround for it.
  

  code-settings-sync/src/service/githubService.ts

  Line 49 in f698ce9

  rejectUnauthorized: false

• The authenticate function is deprecated and we should use the auth option in the constructor of Octokit.
  https://github.com/octokit/rest.js#authentication

How Has This Been Tested?

Tested with "Launch extension" and autoUpdate on and off.

Checklist:

• I have read the contribution guidelines.
• My change requires a change to the documentation and GitHub Wiki.
• I have updated the documentation and Wiki accordingly.

[shanalikhan]

The authenticate function is deprecated and we should use the auth option in the constructor of Octokit.

Can you include this also in PR ?

[LuisUrrutia]

That change it's already in this PR.