INSTUI-4429 fix(ui-time-select): clear input field after setting an empty value

[ToMESSKa]

ISSUE:
In the TimeSelect component, after explicitly setting a value, it cannot be cleared from the input field. When the value is deleted form the input filed and the input field loses focus, the last selected option is reapplied.
Also the onChange does not trigger when input field is cleared.

TEST PLAN:

• go to the "Controlled" TimeSelect example
• select a different value than the current one
• click the input field, delete its current value, and click elsewhere to ensure the input field loses focus
• the input field now should be cleared and have no option selected apart form the placeholder
• onChange should be triggered when input is cleared and loses focus
• test of all the other examples in TimeSelect work as expected
• review the new test
• possible a11y issues should be discussed (eg. with only keyboards, the input field cannot be cleared)

[github-actions]

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[matyasf]

Nice work!
I think that this new behaviour is much more logical, than the old one. (and the old one was even buggy in the uncontrolled behaviour because you could clear the field when the value was not cleared.)

But I'm afraid that introducing this as a fix could break our user's code, since until now it was impossible for the component to return '' as value, it always returned a valid date.
So can you please put this behind a new prop, say allowClearingSelection (it should default to false) to make sure we dont break code?
Also we could make this new behaviour the default one in the next major version, so please add this to our v11-upgrade-guide.md.

PS I could clear the input with just keyboard, what is the a11y concern here?