chore: update dependencies to newer versions, limit jsonschema expose

Mainly to update jsonschema -> reqwest -> hyper to a 1.x version.

Also, this allows to disable the jsonschema dependency. Currently, it is
enabled by default to be compatible with previous versions. But this
can be changed in the next breaking release to exclude it by default.

Signed-off-by: Jens Reimann <[email protected]>