feat: add client.login_with_token

[oleobal]

Summary

This PR adds Client.login_with_token method, which is an alternative to Client.login. Instead of calling a backend endpoint to get a token, just directly use a token.

This is intended for use as part of the single-sign on scheme: SSO users have no password, so they cannot use the current login method. Instead, they will manually retrieve a bearer token and use it with Client.login_with_token.

Open questions:

• maybe it should be use_token (or log_in_with_token)
• maybe we should try contacting the API to make sure the token works

Please check if the PR fulfills these requirements

• If necessary, the changelog has been updated
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• The commit message follows the conventional commit specification
• For any breaking changes, companion PRs have been opened on the following repositories:
  • substra-tests
  • substrafl
  • substra-documentation

[oleobal]

Superfluous