Add `template` and `MR` question to `feature-flag`

What does this MR do?

This does:

• extend issue_url with template
• asks for introduced_by_url
• improved prompt

Impact

$ bin/feature-flag test-flag

>> Please specify the group introducing feature flag, like `group::apm`:
?> group::memory

>> If you have MR open, can you paste the URL here? (or enter to skip)
?> https://gitlab.com/gitlab-org/gitlab/-/merge_requests/38602

>> Open this URL and fill the rest of details:
https://gitlab.com/gitlab-org/gitlab/-/issues/new?issue%5Btitle%5D=%5BFeature+flag%5D+Rollout+of+%60test-flag%60&issuable_template=Feature+Flag+Roll+Out

>> Paste URL of `rollout issue` here, or enter to skip:
?> https://gitlab.com/gitlab-org/gitlab/-/issues/232533
create config/feature_flags/development/test-flag.yml
---
name: test-flag
introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/38602
rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/232533
group: group::memory
type: development
default_enabled: false

Does this MR meet the acceptance criteria?

Conformity

• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team