For a number of DDL statements we want to pass in our own arguments as part of
the WITH statement. This commit adds a parser for such statements, and tests to
ensure that this parser behaves correctly.
Currently, all our WITH options will be namespaced under "timescaledb". In other
words, if we wish to add an option to CREATE INDEX called "foo", it will be used
CREATE INDEX ... WITH (timescaledb.foo='bar')
This should ensure that all our options are consistent with each other, and that
it is obvious which options are ours, and which are not.
