I accidently added 6 hours to my workspace today which was unnecessary, and there's no way for me to wind that back unfortunately. As we implement UI for extending the lease, I suggest we also let the user modify the lease in both directions.

cc @johnstcn

Acceptance Criteria:

• /api/v2/workspaces/:workspace/extend should accept any time greater than or equal to now plus 30 minutes. (fix: allow setting workspace deadline as early as now plus 30 minutes #2328)
• coder bump <workspace> <duration> should set the deadline of workspace named <workspace> to now plus <duration>. Minimum duration is now plus 30 minutes. Deadlines earlier than the currently set deadline should be accepted. (fix: allow setting workspace deadline as early as now plus 30 minutes #2328)
• UI allows editing schedule (plus / minus buttons near the current deadline to add plus/minus some duration)