Adding autocomplete to params using x-data-threescale-name field

[damianpm]

What this PR does / why we need it:

Implements autocomplete of API keys, using the x-data-threescale-name field (see docs)
This PR is a continuation of the job started in #1935, later reverted in #1989

Which issue(s) this PR fixes

https://issues.redhat.com/browse/THREESCALE-4857

Verification steps

• Go to a Service's active docs section: apiconfig/services/2/api_docs
• Create a new OAS v3 using the x-data-threescale-name fields, as described here. You can use this example
• Add a new page or replace the default Documentation page with the following snippet (see docs):

{% content_for javascripts %}
    {{ 'active_docs.js' | javascript_include_tag }}
{% endcontent_for %}

<h1>Documentation</h1>

<div class="swagger-section">
  <div id="message-bar" class="swagger-ui-wrap">&nbsp;</div>
  <div id="swagger-ui-container" class="swagger-ui-wrap"></div>
</div>

<script type="text/javascript">
  (function () {
    var url = "{{provider.api_specs.first.url}}";

    SwaggerUI({ url: url, dom_id: "#swagger-ui-container" });
  }());
</script>

Special notes for your reviewer:

To switch from user_key to app_id / app_key, authentication, go to the edit integration settings page (/apiconfig/services/2/integration) and select an authentication method:

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Admin Portal:

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Developer Portal:

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[josemigallas]

🚀

[didierofrivia]

🎖️