[AGE-164] [Improvement] Speed up the endpoint /get_config

[mmabrouk]

The call to retrieve the configuration takes 1.20 seconds, indicating that 'get_config' is highly unoptimised.

Here's the current process:

• It fetches the base_id.
• It checks permissions.
• It lists the environment for the app_id, which is obtained from the base_id.
• It searches one by one until it finds the correct name.
• It gets the variant_revision_id from the found environment.
• It returns the configuration from that variant.

This process involves a significant number of queries!

_{From SyncLinear.com | AGE-164}