Missing help message when adding new action and Incorrect help message when editing action

Problem/Motivation

While trying to write the test case for #2917917: Change title for create action and edit action routes. I noticed the missing help message when adding a new action and incorrect help message when editing action. For example, Add and Edit screen of "Redirect to URL" action.

Add action screen:

Whilst there is a mistake in the help message. Help message refers to Description field while there is no Description field on that screen. It should refer to Label field.

Edit action screen:

Proposed resolution

1. I think it is a good idea to show same help message when adding new action because help message recommends editing the Label field.
2. Update the help message to refer to the Label field instead of the Description field.

Remaining tasks

Write patch.

User interface changes

1. Make correction in help message.
2. Display help message on add action screen as well.

API changes

N/A

Data model changes

N/A