Remove custom chart steps feature

[rak-phillip]

Summary

This removes the ability to add custom steps while installing charts.

Several issues with this feature were uncovered while reviewing #12010. Most notably, custom steps would fail to render if specific top-level variables (label, subtext) weren't defined. Since this feature does not appear to be in active use, we decided to remove it at this point.

Fixes #11898

Occurred changes and/or fixed issues

• Remove the ability to add custom chart steps
• Add markRaw to dynamically rendered component to prevent Vue from warning about adding reactivity to components that don't need it

Areas or cases that should be tested

• Installing charts

Areas which could experience regressions

• Installing charts

Screenshot/Video

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
• The PR has a Milestone
• The PR template has been filled out
• The PR has been self reviewed
• The PR has a reviewer assigned
• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes

[mantis-toboggan-md]

LGTM