Top Soil Matches list needs loading indicator

[CourtneyLee333]

When the Top Soil Matches list is loading, we need to indicate that status to the user. A good example is when you edit site data and return to this screen, the Top Soil Matches section is disappeared and doesn't display for 5+ seconds:

[knipec]

Closing this, I'm planning to handle all loading indicator stuff as part of https://github.com/techmatters/terraso-product/issues/895