[Enhancement] Overhaul indexing to be more efficient (#540)

* WIP - created methods for breaking on existing media

* WIP - got everything hooked up for POC

* Add some docs, tests

* Refactors

* Updated TODO

lib/pinchflat_web/controllers/sources/source_html/actions_dropdown.html.heex

@@ -54,7 +54,7 @@
     <.link
       href={~p"/sources/#{@source}/force_index"}
       method="post"
-      data-confirm="Are you sure you want to force an index of this source? This isn't normally needed."
+      data-confirm="Are you sure you want index all content from this source? This isn't normally needed."
     >
       Force Index
     </.link>