Add feature flag for checking hosted domain

[matheuscscp]

Description

Add a feature flag to toggle hosted domain check.

Motivation and Context

I have a deployment of Will.IAM where I tried to override the config oauth2.google.hostedDomains through the env. var passing the empty string so I could receive an empty string slice from Viper (empty list of hosted domains), but Viper or Golang thinks the env. var. is not set, instead of understanding it is set to the empty string, and fallbacks to the default config ({domain1, domain2} in the default config file config/local.yaml).

How Has This Been Tested?

Manually in my machine.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code has tests.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

Release strategy