docs(ui-dialog): add a11y clarifications to Dialog docs

[ToMESSKa]

Closes: INSTUI-4293, INSTUI-4291

ISSUES:

• the form labels in the dialog example are not descriptive enough
• the Dialog example does not have a role or appropriate description

TEST PLAN:

• when opening the Dialog example, the screen reader should announce that it is a dialog and read the dialog's label (e.g., "Full name form").
• input labels should be descriptive in the example, such as "First name" instead of just "First", when using a screenreader
• review the added recommendations for dialog accessibility

[github-actions]

PR Preview Action v1.4.8
Preview removed because the pull request was closed.
2024-11-22 13:21 UTC

[matyasf]

nice work :)