QA: Allow registration when LDAP is enabled

What does this MR do?

Lets the QA framework register a user regardless of whether LDAP is enabled.

When LDAP is enabled the names of the tabs on the login page are different from when LDAP is disabled. The framework wasn't able to switch to the register tab because it was missing a selector.

It also wasn't detecting the current tab correctly because it looked for a 'Sign in' button, which is present on the standard tab as well as the LDAP tab.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides