Add OIDC_ROLES_MAPPING support

[mihaivint]

Description

This add support for OIDC_ROLES_MAPPING environment variable:

OIDC_ROLES_MAPPING='{"RoleMap-Admin": "Admin", "RoleMap-Editor":"Editor", "RoleMap-Owner":"Owner","RoleMap-Viewer":"Viewer"}'

#5052

How Has This Been Tested?

Using Vault OIDC provider using the following scope template for OIDC provider:

SCOPE_TEMPLATE='{
"username": "user",
"email": "test@email.com",
"user_roles":["RoleMap-Admin","RoleMap-Editor"]
}'

In case OIDC_ROLES_MAPPING is not defined user_roles remains with normal behaviour and should look like this:

SCOPE_TEMPLATE='{
"username": "user",
"email": "test@email.com",
"user_roles":["Admin","Editor"]
}'

Checklist

• The PR is tagged with proper labels (bug, enhancement, feature, documentation)
• [ x] I have performed a self-review of my own code
• I have added unit tests that prove my fix is effective or that my feature works
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

[mihaivint]

Note that if mapping variable is not defined it maintains the user_roles behaviour

[dy46]

can you add unit tests for this? the code looks good otherwise

[mihaivint]

Added, but that section is pain to test without rest of the code.