Add validation to prevent InvalidCacheKey when fetching resources

[kelvin-muchiri]

Environmental Information

• Onadata version: v3.17.0

Problem description

When an invalid username is used on endpoint /api/v1/profiles/{user} or an invalid primary key is used on endpoint /api/v1/projects/{pk}, the exception InvalidCacheKey is raised

Expected behavior

The API should respond with a 404 status code.

Steps to reproduce the behavior

Try accessing the endpoint /api/v1/profiles/{user} with a username that contains spaces such as /api/v1/profiles/john doe. The API responds with a status code of 500

Additional Information

Logs, related issues, weird / out of place occurrences, local settings, possible approach to solving this...