Annotations: "Create new category" button in modal should be disabled when text field is blank or characters don't meet req's

[liaprins-czi]

Currently, the "Create new label" button within the modal behaves as expected:

• disabled at start, before type any characters
• disables when delete all characters I had typed, so it is an empty field again
• disables when I have a types a duplicate name of an existing label

However, the "Create new category" button within its modal does not disable ever.

Also, both buttons should disable if I type an un-allowed character (e.g. too many spaces in a row, etc); not sure if this is the current behavior because I'm waiting to see that PR.