fix(OAS3): relative urls (#5341)

* Added tooling for appending OAS3 relative URLs to selected Server

Info
* Terms of service URL
* Contact URL
* License URL
* External Docs URL

Tag
* Tag External Docs URL

Operation
* Operation External Docs
** Operation Tag


Co-authored-by: Tim Lai <timothy.lai@gmail.com>

src/core/components/operation.jsx

@@ -2,6 +2,7 @@ import React, { PureComponent } from "react"
 import PropTypes from "prop-types"
 import { getList } from "core/utils"
 import { getExtensions, sanitizeUrl, escapeDeepLinkPath } from "core/utils"
+import { buildUrl } from "core/utils/url"
 import { Iterable, List } from "immutable"
 import ImPropTypes from "react-immutable-proptypes"
 
@@ -81,6 +82,7 @@ export default class Operation extends PureComponent {
       schemes
     } = op
 
+    const externalDocsUrl = externalDocs ? buildUrl(externalDocs.url, specSelectors.url(), { selectedServer: oas3Selectors.selectedServer() }) : ""
     let operation = operationProps.getIn(["op"])
     let responses = operation.get("responses")
     let parameters = getList(operation, ["parameters"])
@@ -127,14 +129,14 @@ export default class Operation extends PureComponent {
                 </div>
               }
               {
-                externalDocs && externalDocs.url ?
+                externalDocsUrl ?
                 <div className="opblock-external-docs-wrapper">
                   <h4 className="opblock-title_normal">Find more details</h4>
                   <div className="opblock-external-docs">
                     <span className="opblock-external-docs__description">
                       <Markdown source={ externalDocs.description } />
                     </span>
-                    <Link target="_blank" className="opblock-external-docs__link" href={sanitizeUrl(externalDocs.url)}>{externalDocs.url}</Link>
+                    <Link target="_blank" className="opblock-external-docs__link" href={sanitizeUrl(externalDocsUrl)}>{externalDocsUrl}</Link>
                   </div>
                 </div> : null
               }