Continue refactoring of API #1405 in remaining files

[totycro]

The api refactoring #1405 introduced a new way of writing APIs. The following two files have not been transformed yet since the change set was already massive:
https://github.com/geopython/pygeoapi/blob/master/pygeoapi/api/__init__.py#L689
https://github.com/geopython/pygeoapi/blob/master/pygeoapi/admin.py#L160%7C

As mentioned in this comment in the review of the PR, these should now be addressed: #1405 (comment)

Transforming the so would allow us to delete some code such as @pre_process and APIRequest.with_data and have a more uniform code base.