Update internal links in API documentation

- Modified links in the OSS and Pro API sections to remove unnecessary README.md suffixes, ensuring cleaner and more direct navigation to the documentation.

This update aims to enhance the clarity and usability of the API documentation.

Author: strickvl

docs/book/api-docs/toc.md

@@ -4,7 +4,7 @@
 
 ## OSS API
 
-* [OSS API](oss-api-docs/README.md)
+* [OSS API](oss-api-docs)
     * [Artifacts](oss-api-docs/v1/artifacts.md)
     * [Artifact versions](oss-api-docs/v1/artifact-versions/README.md)
         * [Batch](oss-api-docs/v1/artifact-versions/batch.md)
@@ -55,7 +55,7 @@
 
 ## Pro API
 
-* [Pro API](pro-api-docs/README.md)
+* [Pro API](pro-api-docs)
   * [API reference](pro-api-docs/api-reference/README.md)
     * [Tenants](pro-api-docs/api-reference/tenants/README.md)
       * [Deploy](pro-api-docs/api-reference/tenants/deploy.md)
@@ -105,4 +105,4 @@
       * [Resource members](pro-api-docs/api-reference/rbac/resource-members.md)
     * [Server](pro-api-docs/api-reference/server/README.md)
       * [Info](pro-api-docs/api-reference/server/info.md)
-  * [Pro API Specification](https://cloudapi.zenml.io/openapi.json) 
+  * [Pro API Specification](https://cloudapi.zenml.io/openapi.json)