Following zack's work on T735, this change introduces an actual SWH lister for
SourceForge.
SourceForge provides a main sitemap that lists sharded sitemaps, which
themselves list pages. Each page belongs to a project (or sub-project,
though those are rare), information about which can be found by querying
a REST API, which gives us the list of any and all VCS used for said
project. Both sitemaps and pages have a "last modified" timestamp that
will be used in a future patch to implement incremental listing.
More precise information can be found as inline comments or docstrings.
Listers are declared as plugins via the `swh.workers` entry_point.
As such, the registry function is expected to return a dict with the
`task_modules` field (as for generic worker plugins), plus:
- `lister`: the lister class,
- `models`: list of SQLAlchemy models used by this lister,
- `init` (optionnal): hook (callable) used to initialize the lister's state
(typically, create/initialize the database for this lister).
If not set, the default implementation creates database tables (after
optionally having deleted exisintg ones) according to models declared in
the `models` register field.
There is no need for explicitely add lister task modules in the main
`conftest` module, but any new/extra lister to be tested must be registered
(the tested lister module must be properly installed in the test environment).
Also refactor a bit the cli tools:
- add support for the standard --config-file option at the 'lister' group
level,
- move the --db-url to the 'lister' group,
- drop the --lister option for the `swh lister db-init` cli tool:
initializing (especially with --drop-tables) the database for a single
lister is unreliable, since all tables are created using a sibgle MetaData
(in the same namespace).
also add a cli group named 'lister' for the sake of consistency with
other swh packages and rename the command as 'db-init', like:
swh lister db-init LISTER [...]
