msw: add policy mock handlers

[deer-wmde]

Note

needs merge & rebase of #1186

Adds basic versions of missing policy mock handlers for viewing the current policies.

• GET /api/v1/policies/terms-of-use
• GET /api/v1/policies/terms-of-use/by_active_from/2022-01-01
• GET /api/v1/policies/terms-of-use/current
• GET /api/v1/policies/terms-of-use/upcoming
• GET /api/v1/policies/hosting-policy
• GET /api/v1/policies/hosting-policy/current
• GET /api/v1/policies/hosting-policy/upcoming

note: due to the current implementation these will need to be adjusted when we add new (current/upcoming) policies. I'm not sure if a more dynamic implementation is worth it.

Compared with the current api routes I noticed in general the coverage of the mocks is not including these endpoints (which is probably fine? as they need different means of testing)

• /api/v1/policy_acceptances - requires ability of mocking different data scenarios
• /api/wiki/profile - could be implemented for a successful store response but re-implementing persistence is as i understand it currenlty not needed

not ui relevant:

• /api/wiki/deletedWikiMetrics
• /api/wikiConversionData
• /api/reusePrototype

https://phabricator.wikimedia.org/T436954

[github-actions]

Deployment previews on netlify for branch refs/pull/1199/merge will be at the following locations (when build is done):

• UI with mock store: https://d7bc0b574d-mock--wbstack-ui.netlify.app/
• UI pointing to prod: https://d7bc0b574d-prod--wbstack-ui.netlify.app/