🚩 PR: Added new Button Step action block

[elsoazemelet]

Closes #775

• Added button step action block, that works with button mode (2-step, 3-step)
• Additional steps can be added similiarly to if condition blocks
• The displayed step name, and the code on grid should update dynamically, when steps are added/removed

[github-actions]

Visit the preview URL for this PR (updated for commit 4788319):

https://grid-editor-web--pr782-feat-buttonstep-vse7auqv.web.app

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[SukuWc]

Looks promising, only need couple of minor tweeks:

• Add "Add Action" helper box similar to all other special action blocks
  
• Action picker menu should not recommend nesting of Button Step actions, please remove this option from the list when it it would cause nesting