Optimise new credentials dialog

[timja]

Optimises the simple case where someone only has one domain so they don't need to click global for no reason

Fixes #1015

If I have multiple domains:

If I delete the domain then click on Add credentials the dialog pops straight up:

Testing done

Manually tested with single domain and multiple domain and added automated regression tests

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• Ensure that the pull request title represents the desired changelog entry
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[janfaracik]

Tested and working as expected - looks good to me!