Allow more if statements in templates

[anikaweinmann]

With https://github.com/actinia-org/actinia-module-plugin/pull/36 you can use in a template a if statement to check if a variable is defined or not, e.g.

{
    "id": "if_statement",
    "description": "Placeholder json file with if statement",
    "template": {
        "version": "1",
        "list": [
            {
                "module": "r.mapcalc",
                "id": "r.mapcalc_test",
                "inputs": [
                    {% if region_union is defined %}
                    {
                        "param": "region",
                        "value": "{{ region_union }}"
                    },
                    {% endif %}
                    {
                        "param": "expression",
                        "comment": "output = r.mapcalc result, string; value = raster value (default=0.428), float",
                        "value": "{{ output }} = {{ value|default(0.428) }}"
                    }
              ]
            }
        ]
    }
}

If the variable region_union is only used for the checking and not used as value for the region, the variable would not be listed by requesting the actinia-module. This should be changed.

Also other if statements should be supported e.g.:

{
    "id": "different_if_statements",
    "description": "Placeholder json file with different if statements as example",
    "template": {
        "version": "1",
        "list": [
            {%- if "test1" in test_list or "test2" in test_list -%}
            {
                "module": "r.mapcalc",
                "comment": "if to check if a sting is in a list",
                "id": "r.mapcalc_test",
                "inputs": [
                    {
                        "param": "expression",
                        "value": "test_list_result = 5"
                    }
              ]
            },
            {%- endif -%}
            {%- if "var" == "test" -%}
            {
                "module": "r.mapcalc",
                "comment": "if to check var is 'test'",
                "id": "r.mapcalc_test",
                "inputs": [
                    {
                        "param": "expression",
                        "value": "test_var_result = 5"
                    }
              ]
            },
            {%- endif -%}
            {%- if "var2" == "True" -%}
            {
                "module": "r.mapcalc",
                "comment": "if to check if var2 is True",
                "id": "r.mapcalc_test",
                "inputs": [
                    {
                        "param": "expression",
                        "value": "test_var2_result = 5"
                    }
              ]
            },
            {%- endif -%}
            {
                "module": "r.mapcalc",
                "id": "r.mapcalc_test",
                "inputs": [
                    {% if region_union is defined %}
                    {
                        "param": "region",
                        "comment": "if to check if a variable is set",
                        "value": "union"
                    },
                    {% endif %}
                    {
                        "param": "expression",
                        "comment": "output = r.mapcalc result, string; value = raster value (default=0.428), float",
                        "value": "{{ output }} = {{ value|default(0.428) }}"
                    }
              ]
            }
        ]
    }
}