Disable add column button when limit has been reached

[bjarnef]

In Umbraco Forms v8.7.0 the column functionality has now been updated, so it has a max limit. #520

However when max limit is reached, it would be great to disable the button "Add Column", e.g. use ng-disabled.
Otherwise editor may wonder why nothing happens when clicking the "Add Column" and 12 columns are added.

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This item has been added to our backlog AB#11274

[nul800sebastiaan]

Sounds like a good idea, I've added it to the list for @AndyButland to have a look at when he has some time. 👍

[AndyButland]

Resolved in the linked PR and due in 8.7.2,