Refactor repository out of Docker entrypoint

[tomkralidis]

Overview

This PR moves RDBMS specific functionality out of the Docker entrypoint into pycsw.core.repository. This allows for repository backends that are not PostgreSQL/SQLite to spin up as expected (following pycsw.core.repository functions).

This PR also moves the query mappings out of OGC API - Records code into the repository as well.

Finally, PL/Python support is removed, given most PostgreSQL installs currently would have PostGIS more easily.

As a result, pycsw.core.repository is a bit more self-contained.

cc @epifanio

Related Issue / Discussion

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Additional Information

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Contributions and Licensing

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• [x] I'd like to contribute [feature X|bugfix Y|docs|something else] to pycsw. I confirm that my contributions to pycsw will be compatible with the pycsw license guidelines at the time of contribution.
• [x] I have already previously agreed to the pycsw Contributions and Licensing Guidelines

[epifanio]

If the DB is not present in the configuration - the sysytem will not start.

My config for the repository section looks like:

[repository]
database=None
table=None
source=pycsw.plugins.repository.solr_metno.SOLRMETNORepository
filter=http://SOLR-IP:8983/solr/adc
adc_collection=ADC
MMD_XSL_DIR=/usr/local/share/mmd/xslt/

➜  CSW_ADC git:(master) ✗ docker run -it -v $(pwd)/test.cfg:/etc/pycsw/pycsw.cfg epinux/pycsw:master
INFO:pycsw.core.repository:Creating database None
DEBUG:__main__:Could not parse SQLAlchemy URL from string 'None'
DEBUG:pycsw.core.config:Initializing static context
INFO:pycsw.core.repository:creating new engine: None
Traceback (most recent call last):
  File "/usr/local/bin/entrypoint.py", line 144, in <module>
    launch_pycsw(config, workers=workers, reload=args.reload)
  File "/usr/local/bin/entrypoint.py", line 82, in launch_pycsw
    repo = Repository(pycsw_config.get("repository", "database"),
  File "/home/pycsw/pycsw/pycsw/core/repository.py", line 107, in __init__
    self.engine = Repository.create_engine('%s' % self.database)
  File "/home/pycsw/pycsw/pycsw/core/repository.py", line 76, in create_engine
    engine = create_engine('%s' % url, echo=False, pool_pre_ping=True)
  File "<string>", line 2, in create_engine
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/deprecations.py", line 375, in warned
    return fn(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/create.py", line 514, in create_engine
    u = _url.make_url(url)
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/url.py", line 738, in make_url
    return _parse_url(name_or_url)
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/url.py", line 799, in _parse_url
    raise exc.ArgumentError(
sqlalchemy.exc.ArgumentError: Could not parse SQLAlchemy URL from string 'None'

@tomkralidis