feat: respond with active task types within heartbeat

[erhant]

Currently the heartbeat response is simply a signed UUID. We should also return the active task types as an array of strings, i.e. ['synthesis', 'taskfoobar'].

[erhant]

This may wait for more updates on Admin node-side of things

[erhant]

Doing this will actually help solve the issue of #34 as follows:

Each worker will have their own busy lock that they can read or write from, e.g. SynthesisBusy or SearchBusy. For example, consider the flow:

1. Node is not busy at all, it responds to heartbeat for two tasks AAA, BBB with the type of provider that it runs.
2. Admin node selects Node for task AAA, and sends it.
3. Node becomes AAABusy = true but still BBBBusy = false.
4. When a heartbeat is made, the Node responds with only BBB because it is not busy with that.

Now the thing is, what if the node can't process AAA and BBB at the same time? E.g. they both use Ollama so they cant be processed in parallel. For this case, the node will also return the provider details within the heartbeat, telling the admin AAA-Ollama and BBB-Ollama.

Admin knows that it cant be doing both at the same time, so it will only respond with one task.

[erhant]

With #51 the only active task type is that of the workflow. So instead, we will return metadata related to models.