feat: Introduce the PAT authentication mode for www.gandi.net connector

[Angak0k]

Description

The www.gandi.net connector offered by the pluggin allow only the api-key way to authenticate connection.
Unfortunately, this way of authentication is now deprecated (see here).
This PR introduce an alternative mode for authentication : Personal Access Token (PAT), the way recomended by gandi to authenticate their APIs.

note: in order to make this change non breaking, the former configuration is still working with the new version - even if the word "Token" used in the former configuration was not really appropriate to define an API-KEY.

Suggested changelog entry

• Introduce a select component in configuration to choose between api-key & personal access token
• Use the api described in the Gandi's up to date documentation
• rework the way errors are managed (test the http response code instead of inspecting response message)

Related issues/external references

Fixes #

Types of changes

• Bug fix (non-breaking change which fixes)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
  • This change is only breaking for integrators, not for external standards or end-users.
• Documentation improvement

PR checklist

• I have checked there is no other PR open for the same change.
• I have read the [La ligne directrice pour contribuer à ce projet / Contribution guidelines for this project).
• I grant the project the right to include and distribute the code under the GNU.
• I have verified that the code complies with the projects coding standards.