Enhance/hdx-api

[nifedara]

What does this PR do?

Enhances documentation quality

Makes updates to HDX endpoints

• I added 422 response and all other responses and examples
• I removed the trailing slash from the endpoints
• Contributes to resolving this issue: Enhance API documentation and examples hotosm/raw-data-api#219

Consideration :

• For consistency in response, I updated the code for the HTTPException messages to follow the error model. e.g {detail["msg": ""]} instead of just {detail[""]}. I did this without discarding the existing messages
• I used black formatter to format the code

How to test?

• Clone this repo
• Follow Docker Installation Guide or local installation guide
• Shoot the server up and view the Documentation changes on your localhost