feat: add casesensitive support

[ninoseki]

This is a proposal to add CASESENSITIVE support in tag fields.

Tag fields are case-insensitive by default. But it's configurable by setting CASESENSITIVE and I believe there is a use case for it. (At least I have it)
This PR makes it possible to set CASESENSITIVE in a schema by setting casesenstive option in a field like what sortable does.

  class Member(BaseHashModel):
      id: int = Field(index=True, primary_key=True)
      first_name: str = Field(index=True, casesensitive=True)
      ...


Member.find(Member.first_name == "andrew").all()
# hits 0 members because the field is case-sensitive

[slorello89]

LGTM 👍 , just made the case_sensitive snake case to be consistent with other fields in the Field function (ironic given I'm adding startswith and endswith in another pr, but a bit more consistent all the same.) Thank you for submitting this!