Added polykey auth login command

[aryanjassal]

Description

This PR adds the polykey auth login command, which takes in an encoded JWT, signs it, and returns the new token. This is meant to verify the identity of the node, which would be as part of a returned field labelled nodeId.

Issues Fixed

• Addresses Create a polykey auth login command #408

Tasks

• 1. Create polykey auth subcommand
• 2. Create polykey auth login command
• 3. Integrate AuthSignToken handler from Polykey
• 4. Write tests for this behaviour

Final checklist

• Domain specific tests
• Full tests
• Updated inline-comment documentation
• Lint fixed
• Squash and rebased
• Sanity check the final build

[tegefaulkes]

Some small comments.