[ModularTable] Add unique row identifiers


After implementing the above it would be easier to test if we could select rows based on some criteria, a `data-test` prop so that we can isolate the 'parent' of grouped rows. It appears that to add such a feature we have to extend the `getRowProps` function.

Using a data driven approach as discussed in the [previous issue](https://github.com/canonical-web-and-design/react-components/issues/440) we could add a prop to the row data that we would inspect to generate this value. There is already precedent for this with the `useExpand` plugin and `subRows.

A data object might look like...
```javascript
const data = {
application: "glance",
operationID: "17 / openstack-upgrade",
rowProps: {
"data-test": "parent-row-glance",
},
};
```

Another approach would be to allow a custom `getRowProps` function to be passed in as in the following examples. This allows for more flexibility but increases the API flexibility which we've previously discussed is undesirable at this time.

ex) https://github.com/tannerlinsley/react-table/blob/master/examples/data-driven-classes-and-styles/src/App.js
ex) https://jbetancur.github.io/react-data-table-component/?path=/story/conditional-styling--conditional-rows