Refactor: Updated naming from resources to endpoints

[Pixelao]

Updated naming from resources to endpoints

With the v5.0.0 release, Resources concept disappears to adopt Endpoints.

This pull request tries to update these concept in the names of the properties, mainly in the tests, but also in some areas of the project where it had not yet been updated.

Changes:

• Updated property names that still reference resources and not endpoints
• Updated README comment talking about resources to endpoints.

[ksvirkou-hubspot]

Thanks for your efforts!