title: Editable and non-editable some ag-grid cells dynamically
body: <p>I have to implement editable/non-editable of the corresponding cells in a  particular row depending on datatype selection. When we select datatype="NUMERIC" then it should be editable particular that cell in a row only under Min and Max column instead of full column.</p>
  
  <pre><code>Example
  ```
      $scope.gridOptions.onCellValueChanged = function(event) {
          if (event.colDef.field === 'validation_type') {
              if (event.newValue.name === 'NUMERIC') {
                  event.columnApi.getColumn('min_value').editable = true;
              }
          }
      }
  ```
  </code></pre>
  
  <p>Then it allow all cells of that column editable. But as per my requirement it should be editable only one particular cell. Please suggest.
  Screenshots:
  <a href="https://i.stack.imgur.com/Zm5UR.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Zm5UR.png" alt="enter image description here"></a></p>