Add missing validations for the REQUIRED configurations.

[chamathns]

Description:
In the Configurations catalog added with asgardeo/asgardeo-tomcat-oidc-agent@0ec2633, some properties are marked as REQUIRED in the app.properties file.
In the config provider or in the DefaultOIDCManager constructor, we need to validate these properties that are marked as REQUIRED.

As of now, validations for the following properties are implemented.

• Consumer Key / Client ID
• Consumer Secret / Client Secret
• Callback URI / Redirect URI
• Scope

Missing validations for the other REQUIRED parameters must also be added there.