APIv4 - Only adjust domain_id if required

[colemanw]

Overview

Alternative to #16911
In 60142ef this field was set to be handled automatically across all entities, however this caused problems with entities like optionValue where it can be NULL. This lifts the default if the field is not required.

Before

In all api4 entities, domain_id field not required and given default value.

After

In all api4 entities, domain_id field not required and given default value only if required in the database.

[civibot]

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[seamuslee001]

Looks good to me merging

[eileenmcnaughton]

nice!