Fix how the RECORDS_REST... config is injected in search template

[ntarocco]

format_config macro in views.py

The configuration of the endpoint URL /api/records and the facets/sort options is now taken from the RECORDS_REST_ENDPOINTS config, search_index field. See Jinja macro:

@blueprint.app_template_filter("format_config")
def format_config(config, endpoint_name):
    """Create config JSON dump for Invenio-Search-JS with React-SearchKit."""
    search_index = (
        config.get("RECORDS_REST_ENDPOINTS", {})
        .get(endpoint_name, {})
        .get("search_index", "records")
    )
    facets = dict(aggs=dict(type=dict(terms=dict(field="type"))))

The issue is that in the records-rest, the search_index field might not be defined (automatically retrieved from the search class).

The second issue is that facets works only with terms, the config parsing should changed or enhanced.