fix(issue-alert): bold headers and indent content (getsentry#40975)

Boldens the step headers and indents the step content when the screen
size > small. Tries to make it consistent with
[this](https://sentry.io/organizations/sentry/dashboards/new/widget/new/)
form.

![Screen Shot 2022-11-03 at 11 04 20
AM](https://user-images.githubusercontent.com/39287272/199800715-273fe160-29ab-4ba8-b491-418e6868d42f.png)

Author: Andrew Xue