feat: migrate POST /api/workspaces/:workspace_id/users to API v1

[jfcalvo]

Description

This PR add a new endpoint POST /api/v1/workspaces/:workspace_id/users to create a new user for a workspace.

Changes introduced in this new endpoint compared to the old one:

• Now we must provide the user_id in the body of the POST request instead of adding it in the URL.
• I have changed the create_workspace_user context function so we need an additional change in argilla repo. The PR with the changes on argilla is here: feat: changes related with migrating endpoints from API v0 to API v1 argilla#4807
• As done with previous PRs the returned user doesn't has full_name or workspaces.

Closes #155

Type of change

(Please delete options that are not relevant. Remember to title the PR according to the type of change)

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (change restructuring the codebase without changing functionality)
• Improvement (change adding some improvement to an existing functionality)
• Documentation update

How Has This Been Tested

• Adding new tests for the endpoint.

Checklist

• I added relevant documentation
• follows the style guidelines of this project
• I did a self-review of my code
• I made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I filled out the contributor form (see text above)
• I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)

[frascuchon]

+1