[Fixes #7194] Append data to an existing layer

[mattiagiupponi]

In order to resolve #7194 with this pr I want to:

• Creating new HTML for layer_append and his view
• New helper utility for the tests named create_single_layer for create only a single layer instead of the 10 created by GeoNodeBaseTestSupport
• New validation function for layer_append & layer_replace named validate_input_source which will check for the compatibility between the layer in upload and the information in the catalog. (with tests)
  This will check the attributes of the uploaded file and the GS catalog:

    new_schema_fields = [field.name for field in lyr.schema]
    gs_layer = gs_catalog.get_layer(layer.name)
    if not gs_layer:
        raise Exception(
            _("The selected Layer does not exists in the catalog."))
    gs_layer = gs_layer.resource.attributes
    schema_is_compliant = all([x in gs_layer for x in new_schema_fields])
    if not schema_is_compliant:
        raise Exception(
            _("Please ensure that the layer structure is consistent "
               f"with the file you are trying to {action_type}."))

• function named gs_append_data_to_layer which is responsible for the APPEND call to geoserver

Checklist

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[codecov]

Codecov Report

Merging #7195 (bbac4a8) into master (c1007fc) will decrease coverage by 33.29%.
The diff coverage is 9.89%.

@@             Coverage Diff             @@
##           master    #7195       +/-   ##
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- Coverage   59.07%   25.77%   -33.30%     
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  Files         565      565               
  Lines       39827    40156      +329     
  Branches     5282     5301       +19     
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- Hits        23527    10350    -13177     
- Misses      14935    29376    +14441     
+ Partials     1365      430      -935