Allow sf agent activate to receive version flag

[jefersonchaves]

Given the Agent versioning it would be great if we can allow a parameter to activate a certain version of the agent instead of always the latest.

The enhancement will allow deployments to not impact existing agent version, deploying more frequently. And then re-activating the agent latest version at a later point.

Code as of 23-Sep: https://github.com/forcedotcom/agents/blob/main/src/agent.ts#L520-L522