Implement agent CLI commands that target gRPC functions

[mscottford]

The initial implementation of the CLI language agent "specification" was for the language agents to implement CLI commands that the Freshli CLI would call. gRPC calls replaced those CLI commands for performance reasons. However, it's still handy to invoke those commands from the CLI for troubleshooting purposes.

Since each agent has to implement the same gRPC functions, the CLI can implement the original commands for this purpose. That prevents each language agent from having to implement the exact same logic for parsing parameters from the CLI.

For each command, the first parameter is the short name of the language agent (e.g. dotnet for freshli-agent-dotnet), and the remaining parameters, if any, are the values that will get passed into the gRPC calls as parameters.

• Implement agents validating-package-urls #620
• Implement agents retrieve-release-history #621
• Implement agents stop-server #622
• Implement agents validating-repositories #623
• Implement agents detect-manifests #624
• Implement agents process-manifest #625
• Implement agents start-server #626