Split the large OpenAPI file into multiple files

**Is your feature request related to a problem? Please describe.**
As the file grows, the readability is going low significantly. We should reorganize it by splitting it into multiple files to improve its readability.

**Describe the solution you'd like**
Reference the good [article ](https://davidgarcia.dev/posts/how-to-split-open-api-spec-into-multiple-files/).

