docs: combine api keys and authentication pages (#9172)

* combine-api-keys-and-auth

* remove-old-page-redirect-and-sidebar

* Update docs/docs/Configuration/api-keys-and-authentication.mdx

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* fix-parse-error

* Apply suggestions from code review

Co-authored-by: April I. Murphy <36110273+aimurphy@users.noreply.github.com>

* upto-env-vars

* clarity-in-example

* clarify-user-creation

* specify-which-table

* links

* link text

* environment variable alignment

* environment variable table cleanup

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>
Co-authored-by: April I. Murphy <36110273+aimurphy@users.noreply.github.com>
Co-authored-by: April M <april.murphy@datastax.com>

docs/docusaurus.config.js

@@ -256,8 +256,10 @@ const config = {
             from: "/components-rag",
           },
           {
-            to: "/configuration-authentication",
+            to: "/api-keys-and-authentication",
             from: [
+              "/configuration-api-keys",
+              "/configuration-authentication",
               "/configuration-security-best-practices",
               "/Configuration/configuration-security-best-practices",
             ],