chore: tasks: refactor existing API endpoints to use new data model

[johnstcn]

Blocked by #948

Update existing tasks-related API endpoints to insert data into the new tables:

• GET /api/experimental/tasks/ feat(coderd): use task data model for list coder#20394
• POST /api/experimental/tasks/ feat(coderd): use task data model when creating a new task coder#20275
• GET /api/experimental/tasks/{id} feat(coderd): use task data model when fetching a task coder#20380
• DELETE /api/experimental/tasks/{id} feat(coderd): use new data model for task delete coder#20334
• GET|POST /api/experimental/tasks/{send,logs} feat(coderd): use task data model for send/logs coder#20381
• Add a migration to update existing tasks to the new format chore(coderd/database/migrations): migrate tasks to new data model coder#20434

[johnstcn]

Due to time constraints, we may not have the time to perform a migration.

Suggested approach:

• Create base branch off main
• Create stacked PRs for each endpoint
• Review+merge stacked PRs into 'base' branch
• Cross our fingers and merge

EDIT: less finger-crossing necessary, as migration turned out to be feasible