Confluence Cloud: add and delete labels through the v1 endpoint

[R3gardless]

Problem

ConfluenceCloud.add_page_label(), add_page_labels() and delete_page_label() send POST / DELETE to api/v2/pages/{id}/labels.

The Confluence Cloud v2 API only defines GET for every label path. From Atlassian's own v2 OpenAPI spec (https://dac-static.atlassian.com/cloud/confluence/openapi-v2.v3.json, info.version 2.0.0):

/attachments/{id}/labels        ['GET']
/blogposts/{id}/labels          ['GET']
/custom-content/{id}/labels     ['GET']
/labels                         ['GET']
/labels/{id}/attachments        ['GET']
/labels/{id}/blogposts          ['GET']
/labels/{id}/pages              ['GET']
/pages/{id}/labels              ['GET']
/spaces/{id}/labels             ['GET']
/spaces/{id}/content/labels     ['GET']

There is no label write endpoint in v2 at all, so these three methods cannot work against Cloud today.

Change

• Add a page_labels_write entry to ConfluenceEndpoints.V2 pointing at the v1 path rest/api/content/{id}/label, which is still served on Cloud.
• Use it in add_page_label(), add_page_labels() and delete_page_label(), and send the payload shape v1 expects: [{"prefix": "global", "name": "<label>"}].
• Reading labels (get_page_labels(), get_space_labels()) is unchanged and stays on v2.
• Docstrings now say the write goes through v1 and that the response is the v1 payload (labels in results).

Tests

• tests/test_confluence_v2.py: test_add_page_label, test_add_page_labels, test_delete_page_label now assert the v1 endpoint and payload.
• tests/test_confluence_v2_with_mocks.py: test_add_page_label mocks the v1 endpoint.
• Full suite: 1751 passed, 10 skipped.