Update directory name from MyHub to ChaosHub in the backend server (graphql server)

[namkyu1999]

Currently, our backend codebase uses the term 'MyHub'. However, In production Litmus uses the term 'ChaosHub' now. So our backend codebase use two terms at the same time. To ensure the stability and long-term viability of our codebase, I suggest unifying the terms 'MyHub' to 'ChaosHub'.

The goal of this issue is to update the name from MyHub to ChaosHub in the backend server. This will involve:

• Updating directory name(package name) from myhub to chaoshub
• Updating function names and variable names relevant to myhub
• Changing collection name of myhub to chaoshub in MongoDB
• Updating any related tests and documentation to reflect the changes made.

Additionally, This issue and pr need to ensure that the process does not impact the existing functionality or stability of the application.

[namkyu1999]

This issue is a subtask of #3892 (LFX mentorship)