Create bbctl feature request issue template

With this epic, we're hoping to cut a branch and create a "code freeze" for bbctl feature development, focusing instead entirely on addressing real user feedback that comes up. Therefore, we need a standardized way of soliciting user feedback that isn't as open as "just send us a message on mattermost."

Acceptance Criteria

Create an issue template for feature requests from users. The template should include:

• The template should request some runtime information from users:
  • system information (os, arch, shell)
  • installation method (go install, binary, homebrew)
  • bbctl version --client
• Explanation of requested feature (what the feature should be)
• Simple justification for this behavior (why we should do it)
• General comments and feedback

Feature requests can be formatted in the form

As a [type of user],
I want to [perform some action]
so that [achieve some goal/benefit]