[Julia] Cleanup README docs (#15295)

* [Julia] fix documentation of API authorization in README files

fix hierarchy level + add internal links + align wording across generators

* [Julia] fix anchor links in documentation

Author: tiffmaelite

modules/openapi-generator/src/main/resources/julia-client/README.mustache

@@ -36,11 +36,13 @@ Class | Method
 {{#models}}{{#model}} - [{{{classname}}}]({{modelDocPath}}{{{classname}}}.md)
 {{/model}}{{/models}}
 
+<a id="authorization"></a>
 ## Authorization
-{{^authMethods}} Endpoints do not require authorization.
-{{/authMethods}}{{#authMethods}}{{#last}} Authentication schemes defined for the API:{{/last}}{{/authMethods}}
+{{^authMethods}}Endpoints do not require authorization.{{/authMethods}}
+{{#hasAuthMethods}}Authentication schemes defined for the API:{{/hasAuthMethods}}
 {{#authMethods}}
-## {{{name}}}
+<a id="{{name}}"></a>
+### {{{name}}}
 {{#isApiKey}}- **Type**: API key
 
 Example

samples/client/petstore/julia/README.md

@@ -52,9 +52,12 @@ Class | Method
  - [User](docs/User.md)
 
 
+<a id="authorization"></a>
 ## Authorization
 
-## petstore_auth
+Authentication schemes defined for the API:
+<a id="petstore_auth"></a>
+### petstore_auth
 - **Type**: OAuth
 - **Flow**: implicit
 - **Authorization URL**: http://petstore.swagger.io/api/oauth/dialog
@@ -72,7 +75,8 @@ Example
     api = MyApi(client)
     result = callApi(api, args...; api_key)
 ```
-## api_key
+<a id="api_key"></a>
+### api_key
 - **Type**: API key
 
 Example