xmltodict now raises an error while trying to parse the HTML content
of https://pypi.org/simple/ page.
So use BeautifulSoup HTML parser instead as it is aleady a requirement
of swh-lister and it does not fail parsing the PyPI HTML page.
Also drop no longer used xmltodict in requirements.
Legacy Lister classes from the swh.lister.core mdule are no longer
used in swh-lister codebase so it is time to remove them.
Also remove lister CLI options related to legacy Lister API.
As a consequence, the following requirements are no longer needed:
arrow, SQLAlchemy, sqlalchemy-stubs and testing.postgresql.
Closes T2442
Add swh.lister.utils.throttling_retry decorator enabling to retry a
function that performs an HTTP request who can return a 429 status code.
The implementation is based on the tenacity module and it is assumed
that the requests library is used when querying an URL.
The default wait strategy is based on exponential backoff.
The default max number of attempts is set to 5, HTTPError exception
will then be reraised.
All tenacity.retry parameters can also be overridden in client code.
Streamline production of new listers by aggressively moving core
functionality into progressively inherited (A->B->C) base classes
with the transport layer abstracted.
This should make common individual forge listers straightforward to
produce with minimal customization. Github and Bitbucket listers
can be used as examples of the indexing type.
