Disallow whitespaces in combiner, client, reducer names

[ahellander]

Severity

• [ ] Critical/Blocker (select if the issue makes the application unusable or causes serious data loss)
• [ ] High (select if the issue affects a major feature and there is no workaround or the available workaround is very complex)
• [ ] Medium (select if the issue affects a minor feature or affects a major feature but has an easy enough workaround to not cause any major inconvenience)
• [x] Low (select if the issue doesn't significantly affect the user experience, like minor visual bugs)

Describe the bug We should add validation to the name parameter and disallow names containing whitespace.

https://code.luasoftware.com/tutorials/python/python-click-cli-validate-and-preprocess-arguments/