API Docs: create Authentication page and order sidebar menu (#92900)

* API Docs: create `Authentication` page and order sidebar menu

* fix minor typos

* Update capitalization

We don't capitalize titles as per https://grafana.com/docs/writers-toolkit/write/style-guide/capitalization-punctuation/

* Update docs/sources/developers/http_api/examples/_index.md

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

* Update docs/sources/developers/http_api/authentication.md

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

---------

Co-authored-by: Irene Rodriguez <irene.rodriguez@grafana.com>
Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

docs/sources/shared/developers/authentication.md

@@ -0,0 +1,36 @@
+---
+headless: true
+comments: |
+  This file is used in the following files: developers/http_api/{_index.md,authentication.md}
+---
+
+You can authenticate HTTP API requests using basic authentication, a service account token, or a session cookie (acquired via regular login or OAuth).
+
+### Basic auth
+
+If basic auth is enabled (it is enabled by default), then you can authenticate your HTTP request via
+standard basic auth. Basic auth will also authenticate LDAP users.
+
+curl example:
+
+```bash
+curl http://admin:admin@localhost:3000/api/org
+{"id":1,"name":"Main Org."}
+```
+
+### Service account token
+
+To create a service account token, click on **Administration** in the left-side menu, click **Users and access**, then **Service Accounts**.
+For more information on how to use service account tokens, refer to the [Service Accounts]({{< relref "../../administration/service-accounts/" >}}) documentation.
+
+You use the token in all requests in the `Authorization` header, like this:
+
+**Example**:
+
+```http
+GET http://your.grafana.com/api/dashboards/db/mydash HTTP/1.1
+Accept: application/json
+Authorization: Bearer eyJrIjoiT0tTcG1pUlY2RnVKZTFVaDFsNFZXdE9ZWmNrMkZYbk
+```
+
+The `Authorization` header value should be _`Bearer <YOUR_SERVICE_ACCOUNT_TOKEN>`_.