Fix bug in WPS client: LiteralInputType is missing DefaultValue property

[awst-baum]

This request fixes a bug in the WPS client:
Currently, LiteralInputType doesn't handle a literal input's default value which can be announced by a WPS server with the <DefaultValue> tag in the ProcessDescriptions, see Web Processing Service standard version 1.0.0, Table 25 (page 26).

This fix adds a property for it to LiteralInputType and adapts ProcessDetails to parse it from the ProcessDescriptions.
It also adds an optional unit test that is run if demo_wps_url2 and demo_wps_def_processor are set in .deegree-test.properties. These values have to refer to a processor that has at least one default value for a literal input, e.g. http://www.zoo-project.org/cgi-bin/zoo_loader.cgi?Service=WPS&Version=1.0.0&Request=GetCapabilities and raster-tools-src.cgi-env.Gdal_Warp

[tfr42]

@awst-baum Thank you for your contribution. Unfortunately, it cannot be merged automatically. It cannot be considered for inclusion, before this has been fixed. Please rebase it against the current target branch.

[github-actions]

Thank you for your contribution. Unfortunately, this PR has been inactive for 90 days (see PR stuck workflow). Of course this is not the final word. The PR can become unstuck, for example, by reengaging in the discussion, answering open questions, rebasing, or adding new commits to this PR.