TableNG: Footer enhancements (#102948)

* Table: Footer support for multiple reducers

* fix migrator test output due to required default value

* fix go migration test

* more go test fixes

* fix go tests for footer

* Merge #110062

* update migration dashboard

* Small docs fixes

* Small docs fix

* remove migration method in Go, update js unit test

* add migration dashboard for footer and clean up some issues with countAll

* Footer should always use og rows for calcs

* update footer to be unaffected by filtering and sorting

* more e2es

* add more complex footer to kitchen sink, migrate panel all the way up

* update codeowners for e2e

* relocate footer migration panels and e2es to main 12.2 migration dashboard

* go further with the migration; kill unused fields, rename reducer to reducers

* get the go code up to date, move enablePagination to its own option as well

* add a unit to one of the numeric columns with a footer in kitchen sink

* fix reducers override in kitchen sink migration table

---------

Co-authored-by: Paul Marbach <paul.marbach@grafana.com>
Co-authored-by: Isabel Matwawana <isabel.matwawana@grafana.com>
Co-authored-by: Isabel Matwawana <76437239+imatwawana@users.noreply.github.com>
Co-authored-by: Leon Sorokin <leeoniya@gmail.com>

docs/sources/panels-visualizations/visualizations/table/index.md

@@ -216,14 +216,35 @@ This option is only available when you're editing the panel.
 
 ### Table footer options
 
-Toggle the **Show table footer** switch on and off to control the display of the footer.
-When the toggle is switched on, you can use the table footer to show [calculations](ref:calculations) on fields.
+The table footer displays the results of calculations (and reducer functions) on fields.
+The footer is only displayed after you select an option in the **Calculation** drop-down list:
 
-After you activate the table footer, make selections for the following options:
+{{< figure src="/media/docs/grafana/panels-visualizations/screenshot-table-footer-selector-v12.2.png" max-width="300px" alt="" >}}
 
-- **Calculation** - The calculation that you want to apply.
-- **Count rows** - This option is displayed if you select the **Count** calculation. If you want to show the number of rows in the dataset instead of the number of values in the selected fields, toggle on the **Count rows** switch.
-- **Fields** - The fields to which you want to apply the calculation. Grafana applies the calculation to all numeric fields if you don't select a field.
+There are several calculations you can choose from including minimum, maximum, first, last, and total.
+For the full list of options, refer to [Calculations](ref:calculations).
+
+In the table footer:
+
+- You can apply multiple calculations at once.
+- All calculations and reducer functions are labeled except **Total** when it's the only function applied.
+- The calculations and reducer functions apply to all fields in the table, by default. To control which fields have a calculation or function applied, add the table footer in an override instead.
+- If you enable a mathematical function for a non-numeric field, nothing for that function is displayed for that field.
+
+In the following image, multiple calculations&mdash;**Mean**, **Max**, and **Last**&mdash;have been applied:
+
+{{< figure src="/media/docs/grafana/panels-visualizations/screenshot-table-footer-1-v12.2.png" max-width="750px" alt="" >}}
+
+You can also see in the previous image that the mathematical functions, **Mean** and **Max**, haven't been applied to the text field in the table.
+Only the **Last** function has been applied to that field.
+
+In the following image, the **Total** calculation has been applied, and no label is displayed because it's the only function:
+
+{{< figure src="/media/docs/grafana/panels-visualizations/screenshot-table-footer-2-v12.2.png" max-width="750px" alt="" >}}
+
+{{< admonition type="note">}}
+Calculations applied to cell types like **Markdown + HTML** might have unexpected results.
+{{< /admonition>}}
 
 ### Cell options