Fix vertical alignment of LDAP radio buttons

What does this MR do and why?

On the LDAP synchronization page, for example https://gdk.test:3443/groups/flightjs/-/ldap_group_links, the two radio buttons were vertically misaligned.

This commit fixes this issue by wrapping in a fieldset and applying custom radio classes to increase the contrast.

In addition, I internationalised some strings and changed the case to make them more consistent between them.

Closes #391268 (closed)

Screenshots or screen recordings

Before

After

Screen_Recording_2023-04-14_at_16.30.13

How to set up and validate locally

1. Enable SAAS mode
2. Go to https://gdk.test:3443/groups/flightjs/-/ldap_group_links

MR acceptance checklist

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