default path & content header change for selenium 4

[shaqtsui]

default path & content header change for selenium 4

Description

selenium 4 have changed host path from "/wd/hub" -> ""
also content-type header need to have charset included.
another bug about WDError construction:
json.value -> json

Some test case can not be execute, as the test dendent page is not available anymore.
But manual tests done.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[terasakisatoshi]

@Nosferican @shaqtsui
This PR should be useful for those who want to use selenium 4