Transform: added merge transform that will merge multiple series/tables into one table (#25490)

* wip: added draft of series to rows.

* wip: building dataFrame structure first and then adding data.

* wip: added some refactorings of the seriesToRows transformer.

* did some refactorings to make the code easier to follow.

* added an editor for the transform.

* renamed some of the test data.

* added docs.

* fixed according to feedback.

* renamved files.

* fixed docs according to feedback.

* fixed so we don't keep labels or config values from.

* removed unused field.

* fixed spelling errors.

* fixed docs according to feedback.

docs/sources/panels/transformations.md

@@ -67,6 +67,7 @@ Grafana comes with the following transformations:
   - [Apply a transformation](#apply-a-transformation)
   - [Transformation types and options](#transformation-types-and-options)
     - [Reduce](#reduce)
+    - [Merge](#merge)
     - [Filter by name](#filter-by-name)
     - [Filter data by query](#filter-data-by-query)
     - [Organize fields](#organize-fields)
@@ -93,6 +94,28 @@ After I apply the transformation, there is no time value and each column has bee
 
 {{< docs-imagebox img="/img/docs/transformations/reduce-after-7-0.png" class="docs-image--no-shadow" max-width= "1100px" >}}
 
+### Merge
+
+Use this transformation to combine the result from multiple queries into one single result based on the time field. This is helpful when using the table panel visualization. 
+
+In the example below, we are visualizing multiple queries returning table data before applying the transformation.
+
+{{< docs-imagebox img="/img/docs/transformations/table-data-before-merge-7-1.png" class="docs-image--no-shadow" max-width= "1100px" >}}
+
+Here is the same example after applying the merge transformation.
+
+{{< docs-imagebox img="/img/docs/transformations/table-data-after-merge-7-1.png" class="docs-image--no-shadow" max-width= "1100px" >}}
+
+If any of the queries return time series data, then a `Metric` column containing the name of the query is added. You can be customized this value by defining `Label` on the source query.
+
+In the example below, we are visualizing multiple queries returning time series data before applying the transformation.
+
+{{< docs-imagebox img="/img/docs/transformations/time-series-before-merge-7-1.png" class="docs-image--no-shadow" max-width= "1100px" >}}
+
+Here is the same example after applying the merge transformation.
+
+{{< docs-imagebox img="/img/docs/transformations/time-series-after-merge-7-1.png" class="docs-image--no-shadow" max-width= "1100px" >}}
+
 ### Filter by name
 
 Use this transformation to remove portions of the query results.