Add option to specify other shell(Arg)

[J-Kappes]

• PR Description

• if os.shell is not empty it replaces the default "bash" shell and os.shellArg replaces the default "-c" argument.

• started writing test but don't know how to check stdout or command log.

• Please check if the PR fulfills these requirements

• [x] Cheatsheets are up-to-date (run go generate ./...)
• [x] Code has been formatted (see here)
• [ ] Tests have been added/updated (see here for the integration test guide)
• [x] Text is internationalised (see here)
• [x] Docs (specifically docs/Config.md) have been updated if necessary
• [x] You've read through your own file changes for silly mistakes etc