feat: adding url schema loader functionality

[maticardenas]

Adding functionality for loading a schema from a url path.

This can be useful for situations where you need to load local tests and you hold schemas in a separate repository / server.

• Adding UrlStaticSchemaLoader to handle the cast of the schema content.
• Checking if schema_file_path is an url and assigning corresponding loader accordingly.
• Adding tests.

This is related to issue #282

[codecov]

Codecov Report

Merging #283 (dd3dda1) into master (ef24951) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff           @@
##           master    #283   +/-   ##
======================================
  Coverage    98.6%   98.7%           
======================================
  Files           7       7           
  Lines         461     474   +13     
  Branches       77      77           
======================================
+ Hits          455     468   +13     
  Misses          4       4           
  Partials        2       2           

Impacted Files	Coverage Δ
openapi_tester/loaders.py	95.9% <100.0%> (+0.2%)	⬆️
openapi_tester/schema_tester.py	100.0% <100.0%> (ø)

[sondrelg]

Looks good, but I'd rather not pull in httpx as a dependency for this. Better do use a builtin library like urllib or requests. Otherwise we're forcing users to potentially pull in an extra dependency for no real gain.

[sondrelg]

Looks great @maticardenas 👏