feat(ui): improve InfluxDB user creation

[sranka]

This PR is a part of the solution to #5834. It improves the way how new InfluxDB users are created.

• a confirmation dialog asking for user name and password is shown after clicking Create User, user detail page allowing to setup roles and DB permissions appears after the new user is created
• error notifications are shown when a user name is too short, a password is too short, or the same user name already exists
• the code is simplified to remove useless redux state management
• a few minor bugs are fixed herein as well

• CHANGELOG.md updated with a link to the PR (not the Issue)
• Well-formatted commit messages
• Rebased/mergeable
• Tests pass

[sranka]

@k3yi0 can you please adjust e2e tests to adopt the new implementation