promote process manager concept to the application level

[tomkralidis]

Is your feature request related to a problem? Please describe.
The process manager was initially developed as a means to manage OGC API - Processes jobs. It would be valuable to enable the manager to be able to provide the ability for pygeoapi downstream applications to manage application-level artifacts as needed.

Describe the solution you'd like

• move pygeoapi.process.manager to pygeoapi.manager
• build out documentation accordingly

Describe alternatives you've considered
None

Additional context
None