Validate JSON complex input file paths

[cehbrecht]

Overview

This PR adds explicit path validation for complex inputs. Added tests to show updated behavior.

Related Issue / Discussion

Additional Information

Contribution Agreement

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

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

[coveralls]

coverage: 80.549%. first build — fix-complexinput into main

[cehbrecht]

@tomkralidis when there are no more findings, we can merge and make a new pywps release.

[tomkralidis]

@tomkralidis when there are no more findings, we can merge and make a new pywps release.

+1 thanks @cehbrecht, makes sense.

[cehbrecht]

@Zeitsperre if you like you can make a new pywps release. I'm offline until Monday.