Showing DAGs in folder like structure

### Description The DAGs main page looks messy when we've too many dags. What if we can create a soft foldering around it? I mean a UI-only folder structure to group DAGs. There could be 2 possible ways to group (or maybe more). The first way is grouping via subpaths under DAGS_FOLDER where the actual dag file is present. The second way is via tags. There could be a toggle button at the top to get the flat list structure as we've at present. @bradarndt @ryanahamilton what do you guys think? ### Use case/motivation This feature would help keep the DAGs main page neat and clean. It would also motivate the users to arrange the dags as per their functionalities. ### Related issues _No response_ ### Are you willing to submit a PR? - [ ] Yes I am willing to submit a PR! ### Code of Conduct - [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)