Implement neq query operator

[mcucchi9]

Related Issue(s):

• Query extension: standard neq operator is missing #363

Description:

This PR does two things:

1. Simplify the Operator class in the extensions/query.py module by removing the unused operator method and unnecessary dependencies.
2. Implement the STAC API standard neq query operator, leveraging the neq pgstac opeator, and add related test.

Closes #363

PR Checklist:

• pre-commit hooks pass locally
• Tests pass (run make test)
• Documentation has been updated to reflect changes, if applicable, and docs build successfully (run make docs)
• Changes are added to the CHANGELOG.

NOTE: tests have been run only for pgstac=0.9.9, as per #346.

[bitner]

This is fine, but I will note that this only works because pgstac tries to be very permissive on operators that it accepts, so it will take "ne", "neq", "<>", and "!=" to be the same thing in either a query, cql1 or cql2. This is technically incorrect, but we have decided it is better to be lax in what we accept.

Officially, pgstac only really tries to support CQL2 json and makes a good faith effort to support the query extension (which while not deprecated - for a while it actually was marked as deprecated, but it seems to have risen from the dead - does recommend people to switch to the filter extension with CQL2). It does this by trying to convert query or CQL1 into CQL2, but these transformations are far from fully tested in our unit tests.

It is highly recommended that people shift away from the query extension and from using CQL1 towards CQL2. At some point in the future it is likely that we will deprecate and cease support in pgstac for these.