[core] feat(MultiStepDialog): allow multiple close buttons

[tinopetros]

Fixes #5758

Checklist

• Includes tests
• Update documentation

Changes proposed in this pull request:

• isCloseButtonShown only affects the close button in the header
• showCloseButtonInFooter independently affects the close button in the footer (and now allows the exciting possibility of having a third custom button e.g. to skip the multiple steps of the dialog.
• Updated inline prop docs and omitted tests since there were none for close buttons previously

Reviewers should focus on:

• The separation of isCloseButtonShown and showCloseButtonInFooter and that it works as expected depending on the set props.

Screenshot

[adidahiya]

thanks @tinopetros!