xmltodict cannot parse POM files with multi-byte encoding so prefer to
use the XML parser of BeautifulSoup based on lxml instead.
Also drop xmltodict requirement as it is no longer used in swh-lister
codebase.
The Maven lister retrieves the maven central indexes, exports them in a
convenient text format, and parse them to identify all src archives and
pom files in the maven repository. Then the pom files are downloaded and
analysed to find and yield any scm reference.
Note: This is a new version of the maven lister diff D6133 which takes
into account the initial round of reviews.
Related to T1724
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
Port launchpad lister to the swh.lister.pattern.Lister API.
Last update date of each listed git repositories is now sent to the scheduler.
The lister can work in incremental mode, only modified repositories since
the last listing operation will be returned in that case.
Closes T2992
