Convert Insomnia variables syntax in headers, parameters and form data (#291)

Co-authored-by: Gregory Schier <gschier1990@gmail.com>

plugins/importer-insomnia/tests/fixtures/version-5.input.yaml

@@ -46,6 +46,10 @@ collection:
             name: X-Header
             value: xxxx
             disabled: false
+          - id: pair_ab4b870278e943cba6babf5a73e213e3
+            name: "{{ _.ApiHeaderName }}"
+            value: "{{ _.ApiKey }}"
+            disabled: false
         authentication:
           type: basic
           useISO88591: false

plugins/importer-insomnia/tests/fixtures/version-5.output.json

@@ -127,6 +127,11 @@
             "enabled": true,
             "name": "X-Header",
             "value": "xxxx"
+          },
+          {
+            "enabled": true,
+            "name": "${[ApiHeaderName ]}",
+            "value": "${[ApiKey ]}"
           }
         ],
         "id": "GENERATE_ID::req_d72fff2a6b104b91a2ebe9de9edd2785",