config file for `upterm host` command

[bavarianbidi]

If all the three PRs i've done today got accepted we will get 11 flags to configure upterm host command.
I would like to have the option for using a configuration file beside all the different arguments.

Would you accept a PR for supporting a config file?

Recent PRs which add more flags to upterm host subcommand:

• #182
• #190
• #191
• #192