Incorrect type in `EndpointConfig` for `endpoint` and `endpoint_follow` configuration

[devraj]

Describe the bug
The EndpointConfig class has the following definition:

@dataclass
class EndpointConfig:
    endpoint: str  # partial path to the endpoint e.g. day_category
    endpoint_follow: str | None = None  # partial path to the follow endpoint

which was correct when the project started, however through the lifecycle we have moved to using OptionalHref classes to reference the URLs:

class FeatureEventsRef(AppBaseModel):
    divisions: OptionalHrefMixin = None
    event_groups: OptionalHrefMixin = None
    events: OptionalHrefMixin = None
    updates: OptionalHrefMixin = None

while this won't raise an issue as href is a wrapper on str, this should be properly retrofitted to represent the right type.

To Reproduce
Not applicable as these values are internally populated on discovery.

Expected behavior
NA