This PR adds a package lifecycle and an Executor implementation that attempts to schedule a build of workspaces with autostart configured.
- lifecycle.Executor takes a chan time.Time in its constructor (e.g. time.Tick(time.Minute))
- Whenever a value is received from this channel, it executes one iteration of looping through the workspaces and triggering lifecycle operations.
- When the context passed to the executor is Done, it exits.
- Only workspaces that meet the following criteria will have a lifecycle operation applied to them:
- Workspace has a valid and non-empty autostart or autostop schedule (either)
- Workspace's last build was successful
- The following transitions will be applied depending on the current workspace state:
- If the workspace is currently running, it will be stopped.
- If the workspace is currently stopped, it will be started.
- Otherwise, nothing will be done.
- Workspace builds will be created with the same parameters and template version as the last successful build (for example, template version)
