Logfile rotation and configurable log format

[xkosubek]

Overview

• Added configurable log and date format
• Added support for logfile rotation
• Updated documentation

Related Issue / Discussion

fixes #1389
fixes #1388

Contributions and Licensing

(as per https://github.com/geopython/pygeoapi/blob/master/CONTRIBUTING.md#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pygeoapi. I confirm that my contributions to pygeoapi will be compatible with the pygeoapi license guidelines at the time of contribution.
• I have already previously agreed to the pygeoapi Contributions and Licensing Guidelines

[totycro]

Currently if the mode is set to null in yaml, which would correspond to python None, this would lead to an exception because it would be detected as an unknown mode.

I think the code is fine though, and we could require here in the documentation that mode must only be time|size. If someone doesn't want log rotation, they can just not have the whole rotation block.