Update graphhopper API client

[smonist]

What type of PR is this?

• Feature?
• Bug fix
• Refactor
• Experiment update

Description

• update all dependencies of the project
• use the openapi-generator cli instead of downloading a .jar file from maven
• remove unused generator script
• manually added graphhopper api spec. they seem to have removed the static link. since this package has to be released by hand anyway, i do think this is okay (for now). just redownload the file from the top of their docs before rebuilding the api.