Issue#2323

[MohitPanchariya]

What type of PR is this?

(REQUIRED)

• feature

What this PR does / why we need it:

(REQUIRED)

• This PR introduces an option to include arbitrary help topics to the help message.
• There exists a way to do this for the Root command right now, through the ExtraInfo field,
  but that requires using a custom template. Its a bit cumbersome to use custom templates from a
  users perspective just to print additional help topics.
• Given the use case to have additional help topics seems generic, this PR changes the default
  help templates to conditionally render additional help topics.

Which issue(s) this PR fixes:

Fixes #2323

(REQUIRED)

Testing

(fill-in or delete this section)

Added unit tests to test additional help topics.

Release Notes

(REQUIRED)

The `AdditionalHelpTopics` field can be used to print arbitrary help topics, in addition to the existing
help topics, without the need for a custom help template.