[FEATURE] Add new data type: `UNIT`

[Yury-Fridlyand]

Is your feature request related to a problem?

TIMESTAMPADD and TIMESTAMPDIFF functions in mysql have unit as an argument. See also EXTRACT function.

What solution would you like?

A new data type: UNIT:

1. Not storable and not returnable to user.
2. Not comparable and not castable.
3. Can store multiple units inside, see EXTRACT.
4. For use in few datetime functions only.

What alternatives have you considered?

Use a string instead.

Do you have any additional context?

#722
#855

[Yury-Fridlyand]

Implemented with workaround in

• EXTRACT Add EXTRACT Function To OpenSearch SQL Plugin #1421
• TIMESTAMPADD Add TIMESTAMPADD Function To OpenSearch SQL Plugin #1451
• TIMESTAMPDIFF Add Timestampdiff Function To OpenSearch SQL #1467