[improve][cli]Support for pulsar-shell persistent modes

[sandeep-mst]

Fixes 21194 of apache/pulsar

Motivation

Pulsar shell doesn't support persistent mode for admin, client, config. If we need to run a lot of admin commands for example, we would need to prefix admin each time. This will provide an alternative approach.

Modifications

Modified so that admin, client, config commands individually will launch their own mode and prompt message also gets updated. exit or quit command will exit from the mode to the default mode.
In the admin mode, we can run command topics instead of admin topics.

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• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

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Matching PR in forked repository

PR in forked repository:
cognitree#6

[lhotari]

Good work @sandeep-mst . A few minor review comments.

[nicoloboschi]

I like this idea.

1. I think we should register the new commands like other commands in registerProviders(..) so automatic autocompletion will work for these modes too.

2. I don't understand the title, what do you mean by persistent modes ? I think we need a better name for this feature.

3. We should add docs, at least in the help (might be mitigated by 1.)