Adds a new subcomponent of the agent for queueing up logs until they can be sent over the Agent API.
Subsequent PR will change the agent to use this instead of the HTTP API for posting logs.
Relates to #10534
`agentsdk` depends on `agent/proto` because it needs to get the version to dial.
Therefore, the conversion routines need to live in `agentsdk` so that we can convert to and from the Manifest.
I briefly considered refactoring the agent to only reference `proto.Manifest`, but decided against it because we might have multiple protocol versions in the future, its useful to have a protocol-independent data structure.