Initial vector data support

[Dukestep]

This MR adds initial vector data support, enabling the generation and serving of vector data via the use of MapServer's OGR vector layers support.

Layers with underlying vector data can now be defined in the configuration as such:

RADAR_COVERAGE_RRAI:
    type: polygon
    temporal_config: /path/to/radar_coverage_mmhr_merged_realtime.json
    connection:
        type: OGR
        url: ES:localhost:9200
        data: radar_coverage-mmhr-merged-realtime
        options:
            layer: radar_coverage-mmhr-merged-realtime
    filters:
        - type: datetime
          field: properties.datetime_mapserver
    [...]

The connection key is used to setup the appropriate CONNECTION, CONNECTIONTYPE, CONNECTIONOPTIONS and DATA directives.

Rudimentary filters can be defined as an array of objects under the filter key. If multiple filters are defined, they are concatenated using the operators provided via the operator key in filters subsequent to the first filter defined. If a filter of type datetime is specified, a metadata key is set in order to retrieve the filter and format it accordingly when a request is received, either with the default time value or via the TIME query param value contained in the request.

If the temporal_config key is defined, the temporal metadata is retrieved from a file instead of retrieving it from geomet-data-registry's store.

The wsgi.py application is modified to intercept any MapServer layer objects of type point, line, polygon. If they are time-enabled, the application then verifies that the time is valid given the start/end/interval , and sets the PROCESSING "NATIVE_FILTER=<filter> directive. The rest of the request and response is managed by MapServer.