Replace NotImplementedErrors with MethodErrors

[nickrobinson251]

• MethodErrors convey this same information, with the bonus of showing "closest candidates"
• Since all the functions here belong to the DBInterface namespace (we're not e.g. adding methods to Base functions), the MethodErrors should be particularly helpful
• Furthermore, in a few cases the message in the NotImplementedError may just be incorrect
  • e.g. in

     connect(T, args...; kw...) = throw(NotImplementedError("`DBInterface.connect` not implemented for `$T`"))

    there may be methods for T, but not for the given args
  • this is discussed at the start of this blog https://white.ucc.asn.au/2020/04/19/Julia-Antipatterns.html
  • instead we can just define a function with a docstring and no methods

    """docstring"""
    function connect end

• This also would remove quite a few lines of code at no cost

[quinnj]

Yeah, I'd be fine w/ doing this if you want to put up a PR