Update to VSS 3.1.1

[erikbosch]

In theory this would have been a very small PR but it grew a bit bigger:

• Based on detection that VSS 3.1 lacked a description on one branch (required by databroker) this PR integrated VSS 3.1 instead.
• While testing against kuksa-server it was detected that kuksa client lib for websocket could not handle boolean mappings. This was likely missed in previous testing as testing towards kuksa-server was performed when only a subset of mappings had been added. This has been fixed by using json.dump(value) rather than str(value). Issues created at https://github.com/eclipse/kuksa.val/issues/493
• Related to the boolean-finding, tests and docs have been refactored to use Yaml 1.2 compliant terms for true/false. Even if vss-tools still (implictly) use Yaml 1.1 (which supports e.g. True and False, On and Off) it is better to stick to Yaml 1.1. terms
• Some linter improvements

[SebastianSchildt]

I am wondering, whether it would be better to provide a 3.1.1 AND a 3.0 mapping file. Currently the mapping is not compatible with the the released/3.0 databroker

2023-03-02 16:53:03,447 ERROR dbcfeederlib.databroker: Signal Vehicle.Body.Lights.Backup.IsOn is not registered
2023-03-02 16:53:03,452 ERROR dbcfeederlib.databroker: Signal Vehicle.Body.Lights.Brake.IsActive is not registered
2023-03-02 16:53:03,460 ERROR dbcfeederlib.databroker: Signal Vehicle.Body.Lights.Fog.Rear.IsOn is not registered
2023-03-02 16:53:03,464 ERROR dbcfeederlib.databroker: Signal Vehicle.Body.Lights.DirectionIndicator.Left.IsSignaling is not registered
2023-03-02 16:53:03,467 ERROR dbcfeederlib.databroker: Signal Vehicle.Body.Lights.DirectionIndicator.Right.IsSignaling is not registered

I guess we could just copy the file and remove the Light signals. At least then, in case of problems, we can tell people "use the 3.0 mapping", instead of "go to some older version of DBC feeder" (that may have other problems)