rpk connect: show rpk help text with --help/-h

[r-vasquez]

Previously we were displaying only the connect
plugin help text, and not the rpk one. We were
missing the lifecycle commands (install, uninstall, upgrade).

Backports Required

• none - not a bug fix
• none - this is a backport
• none - issue does not exist in previous branches
• none - papercut/not impactful enough to backport
• v24.2.x
• v24.1.x
• v23.3.x

Release Notes

• none

[gene-redpanda]

Is it worth having some func RpkHelp(cmd) that can handle this + the plugin help?

[r-vasquez]

@gene-redpanda part of the plugin installation process is adding the help text of the plugin into rpk, so displaying rpk's help text includes both. This is how it looks now:

$ rpk connect -h                                 
A stream processor for mundane tasks - https://docs.redpanda.com/redpanda-connect

Usage:
  rpk connect [flags]
  rpk connect [command]

Available Commands:
  blobl       Execute a Redpanda Connect mapping on documents consumed via stdin
  create      Create a new Redpanda Connect config
  echo        Parse a config file and echo back a normalised version
  help        Shows a list of commands or help for one command
  install     Install Redpanda Connect
  lint        Parse Redpanda Connect configs and report any linting errors
  list        List all Redpanda Connect component types
  run         Run Redpanda Connect in normal mode against a specified config file
  streams     Run Redpanda Connect in streams mode
  template    Interact and generate Redpanda Connect templates
  test        Execute Redpanda Connect unit tests
  uninstall   Uninstall the Redpanda Connect plugin
  upgrade     Upgrade to the latest Redpanda Connect version

Flags:
  -h, --help   Help for connect

Global Flags:
      --config string            Redpanda or rpk config file; default search paths are
                                 "/home/rvasquez/.config/rpk/rpk.yaml", $PWD/redpanda.yaml, and /etc/redpanda/redpanda.yaml
  -X, --config-opt stringArray   Override rpk configuration settings; '-X help' for detail or '-X list' for terser detail
      --profile string           rpk profile to use
  -v, --verbose                  Enable verbose logging

Use "rpk connect [command] --help" for more information about a command.

[vbotbuildovich]

the below tests from https://buildkite.com/redpanda/redpanda/builds/57814#0193090e-1857-4cae-8d83-6033ca84b165 have failed and will be retried

gtest_raft_rpunit

[vbotbuildovich]

/backport v24.2.x