[SD-558]updated help text and change labels

[yeniatencio]

Jira

https://digital-vic.atlassian.net/browse/SD-558 and https://digital-vic.atlassian.net/browse/SD-22
Testing link: https://nginx-php.pr-1759.content-vic.sdp4.sdp.vic.gov.au/

Problem/Motivation

This PR is covering aceptance criteria from the tickets mentioned above.

1. Rename ‘hero image theme’ field to ‘Page title display style’
2. Change the drop down options to:
   ‘Light’ to ‘Default’
   ‘Dark’ to ‘Reverse blocked text’
3. Update help text to display below the field.
4. Move the field to display after ‘Header styles’ on the Landing page content type
   Scenarios:

• Corner graphics - Default + Reverse blocked text (Both options available and by default "Default" should be selected)
• Full background image - Reverse blocked text only (Only one option should be set)
• CTA - Default only (Only one option should be set)
• Default appearance - Default only (Only one option should be set)
  Note: Previous PR from ticket SD-22 is not needed anymore as this PR is covering that.

Fix

Related PRs

Screenshots

TODO

[vincent-gao]

@yeniatencio ready for test. once the tests pass and approval is received from Jess, it can be merged.