Allow for multiple observers with the same schema

[polymorfiq]

It is currently impossible to have multiple observer configurations that use the same schema.

This is because the Schema Name does not contain ".observers" and so it fails the duplication check that is supposed to allow it. That string is currently contained in the Schema Vendor.

[snowplowcla]

@fingerco has signed the Individual Contributor License Agreement

[alexanderdean]

Thanks @fingerco ! Assigning to @chuwy to review

[rzats]

Included in #80, closing