Fix pay later messaging options

[strangerkir]

Issue: PCP-113.

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Description

Pay Later messaging settings are contained fields related to two types of layout: text and flex. At any moment only one type of field should be displayed, depending on what selected, text or flex.

Steps to test:

1. Log into WP admin.
2. Go to the plugin settings.
3. Enable Pay Later messaging (if not enabled).
4. Check what type of layout is selected.
5. Make sure that only respective options are displayed below the layout select field. For Text: logo, logo position, text color. For Flex: color and ratio. Also, WC help tips next to each field contain info on what type of layout this setting relates to.
6. Try to check/uncheck PayLater messages and save. Make sure the proper fields are displayed each time and no fields displayed if PayLater messaging is disabled.
7. Try to switch layout and save. Make sure you can see proper fields.

Note: There are three sets of settings fields related to Pay Later messages: for checkout, for cart, and for product page. They have the same fields and the same appearance logic described above.

Documentation

• This PR needs documentation (has the "Documentation" label).

Changelog entry

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.

• Fix - Pay Later settings appearance based on selected layout type.

Closes #138.