[Feature] Add Constant providers

[vianneybacoup]

Issue to track the Implemention of Constant providers.

We should be able, for each type listed below, to add either parameters:

• simple value
• list of values
• weighted list of values

String has been done by @bhagenbourger, it is a good example of the expectations for the rest of the types.

• string
• boolean
• date
• timestamp
• integer
• float

[vianneybacoup]

As @bhagenbourger you added more features than expected for the string constant (pure constant parameter, list or weighted list), I'll update this ticket to express those details and new expectations for the other types.