[Terrarium - Providers]: Fix empty structs

[anjanikshree12]

Problem:

• Found a small bug, On registration of providers, we are not yet publishing it, but although being empty, published_on field used to get added in the table as an attribute of an item having empty value, which should not happen until we publish it actually.
• Same for modified_on too.

Solution:

• Added omit_empty in the Struct tags which would avoid the structs to be added as an attribute in the table when it's empty as they get omitted.