This PR adds fields to templates that constrain values for workspaces derived from that template.
- Autostop: Adds a field max_ttl on the template which limits the maximum value of ttl on all workspaces derived from that template. Defaulting to 168 hours, enforced on edits to workspace metadata. New workspaces will default to the templates's `max_ttl` if not specified.
- Autostart: Adds a field min_autostart_duration which limits the minimum duration between successive autostarts of a template, measured from a single reference time. Defaulting to 1 hour, enforced on edits to workspace metadata.
* Changes all public-facing codersdk types to use a plain int64 (milliseconds) instead of time.Duration.
* Makes autostart_schedule a *string as it may not be present.
* Adds a utils/ptr package with some useful methods.
* Adds a `bump` command to extend workspace build deadline
* Reduces WARN-level logging spam from autobuild executor
* Modifies `cli/ssh` notifications to read from workspace build deadline and to notify relative time instead (sidestepping the problem of figuring out a user's timezone across multiple OSes)
* Shows workspace extension time in `coder list` output e.g.
```
WORKSPACE TEMPLATE STATUS LAST BUILT OUTDATED AUTOSTART TTL
developer/test1 docker Running 4m false 0 9 * * MON-FRI 15m (+5m)
```
