Feature: Context's command for switching to previous (old) nats context

[boris-ilijic]

New nats context subcommand that allows cd - or git checkout - type of operation but for NATS context.
This PR implements the logic for switching to the previous (old) nats context using:

• nats ctx previous
• nats ctx -- - (unfortunately wasn't able to make nats ctx - to work)

Example:

$ nats ctx select local-sys                                                                                                                                       
NATS Configuration Context "local-sys"

  Description: localhost sys
  Server URLs: nats://127.0.0.1:4222
     Username: admin
     Password: ********
         Path: /Users/boris/.config/nats/context/local-sys.json

$ nats ctx -- -                                                                                                                                         
NATS Configuration Context "local"

   Description: Localhost
   Server URLs: nats://127.0.0.1:4222
      Username: ruser
      Password: *********
          Path: /Users/boris/.config/nats/context/local.json
  Color Scheme: yellow

$ nats ctx -- -                                                                                                                                               
NATS Configuration Context "local-sys"

  Description: localhost sys
  Server URLs: nats://127.0.0.1:4222
     Username: admin
     Password: ********
         Path: /Users/boris/.config/nats/context/local-sys.json

This PR is still not ready and requires:

• merging Storing name of the previous (old) natscli context jsm.go#485 and updating its dependency
• fixing natscli@main due to breaking changes within jsm.go@main which is present at this moment and is not related to this PR (so please ignore changes within stream_command.go)

[ripienaar]

For the breaking change maye wait for https://github.com/nats-io/natscli/pull/890/files to land then rebase yours ontop.

The missing field was a left over from the beta phases that didnt make it to release so has to go.

[boris-ilijic]

Thanks for info, I'll wait for that PR.
Keep in mind that nats-io/jsm.go#485 needs to be merged also to completely finalize this one.

[boris-ilijic]

PR is ready

[ripienaar]

Nice one thank you!