Support tagging to distinguish multiple projects

[keaxu-exp]

Hi,

As title described. I think this feature will be helpful when:

• managing projects programmatically
• integrating doccano with other jobs/services.

Here are my thoughts:

UI:

DB Models:
add one more table api_tag, with following columns:

id (PK)
text
created_at
project_id (FK)
text_color
background_color

APIs:
GET /projects/{project_id}/tags

response body may look like:

[
  {
    "id": 1,
    "text": "In Progress"
  },
  {
    "id": 2,
    "text": "Completed"
  }
]

POST /projects/{project_id}/tags
GET /projects/{project_id}/tags/{tag_id}
PUT /projects/{project_id}/tags/{tag_id}
PATCH /projects/{project_id}/tags/{tag_id}
DELETE /projects/{project_id}/tags/{tag_id}

Usecases & Scenarios:

We want to integrate doccano with our interval jobs/services. As providing an automated platform, we want annotators explicitly mark a project as 'completed', so that certain downstream jobs can be triggered.

As we serving doccano for multiple internal teams, we also want to attach business-related information to the project, like model names, stakeholder teams, etc.

[Hironsan]

Solved #1301.