add a graph to workspace agents that tracks dependencies between scripts

[SasSwart]

Relates to: coder/coder#10352

In order to track dependencies between coder scripts and other resources during workspace initialisation and runtime, we need a graph implementation inside the workspace agent.

Coder scripts and other consumers of the API may register themselves as vertices of the graph.
When a script changes its own status in this graph, dependent vertices will eventually be notified so that they may begin their own execution if conditions are right to do so. However, this notification is beyond scope for the current issue.

To close this issue, a consumer of the new graph interface must be able to:

• register itself as a vertex in the graph
• register its dependencies and dependents
• update its own status

Beyond scope for this issue:

• notifying dependencies when a status changes
• exposing the graph to the rest of the agent, the cli or to terraform

[SasSwart]

closed by coder/coder#20208