feat(ui): improve InfluxDB role creation

[sranka]

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

• a confirmation dialog asking for a role name is shown after clicking Create Role; A role detail page appears right after the new role is created
• error notifications are shown when a role name is too short, or the same role already exists
• the code is simplified to remove useless redux state management
• a few minor bugs are fixed herein as well
• create dialogs (for both user and role) now visually distinguish valid inputs

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