Don't access oauth2_settings if OAuthLibCore server parameter is prov…

[claytonsingh]

Description of the Change

Dont access oauth2_settings if server parameter is provided

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[n2ygk]

@claytonsingh what is the purpose of this change? How and why would one do this?

[claytonsingh]

I have some specific requirements and am not using this library in INSTALLED_APPS. The methods and classes do provide extensive value though.

[n2ygk]

Please add a use case example to the documentation and add a test.

I can't merge something that doesn't have an clear (to others) purpose.
Thanks.

[dopry]

@claytonsingh bump, do you have time to wrap up this PR? Id be good to get the use case documented and some tests around the feature.