Support OAUTH2 (Client and Password flows only) in RestWorkItemHandler

We are currently supporting apiKey, bearertoken and basic auth mechanism. The target of this Jira is to add Oauth2 support. This will add support for credential and password grant type only. Since authorization and implicit flows requires access to an agent, they will not be probably used widely in workflow.

client id and client secret will be read from environment. property keys are

org.kogito.openapi.client.<service name>.client_id
org.kogito.openapi.client.<service name>.client_secret