Not clear that agent users must not initialize the SDK

[anuraaga]

I think we've had a few reported issues because of an agent user initializing the SDK. We probably don't discourage this enough. We can probably

• Document as soon as we mention an agent artifact the ones that should not be present with it. Notably if we just list the two compatible artifacts, -api and -annotations, we can probably prevent others from being used

• Add instrumentation in the agent to log a very scary warning when the SDK is built

• Move annotations into -api? More of a strawmans but I think ideally either it is in -api, assuming a non-agent solution to using them will come some day, or acknowledge we won't do this in v1 and just move it to .javaagent Maven namespace to make more obvious that the annotations are 1:1 with javaagent, it would be more obvious for users I think

[trask]

Closing, can revisit later if anyone has renewed interest.