Add Agent Label to prefect.context.config

[joeschmid]

Current behavior

From within a task, basic info about an Agent is available via prefect.context.config:

{'cloud': 
    {'agent': 
      {'level': 'INFO',
       'name': 'agent',
       'resource_manager': <Box: {'loop_interval': 60}>},

Proposed behavior

If running multiple Agents (with Environment Labels), having access to the label setting for the Agent that kicked off execution would be useful.

Example

A Flow that monitors a k8s/Dask cluster could include the environment label in its alerts, e.g. "Found 100 nodes running in the staging environment" where staging was the label the Agent was started with.