Document Git Credential Manager as alternative to personal access tokens

Git Credential Manager is a user-friendly alternative to personal access tokens for secure passwordless authentication to HTTPS remotes that uses GitLab OAuth.

GitLab should document Git Credential Manager as an alternative to personal access tokens.

More about GCM:

• https://stackoverflow.com/questions/35942754/how-can-i-save-username-and-password-in-git/71284566#71284566
• https://github.com/GitCredentialManager/git-credential-manager/blob/main/docs/gitlab.md
• https://github.blog/2022-04-07-git-credential-manager-authentication-for-everyone/

Docs to update:

• https://docs.gitlab.com/ee/user/profile/account/two_factor_authentication.html#use-personal-access-tokens-with-two-factor-authentication

  When 2FA is enabled, you can’t use your password to authenticate with Git over HTTPS or the GitLab API. You must use a personal access token instead.

• https://docs.gitlab.com/ee/gitlab-basics/start-using-git.html#clone-with-https

  If you have 2FA enabled for your account, you must use a Personal Access Token

• https://docs.gitlab.com/ee/user/profile/personal_access_tokens.html

  Personal access tokens are: Required when two-factor authentication (2FA) is enabled.