Support main+sub stream exports (#24193)

* Support multi resolution exports

* Fix decoder text

* Add dropdown and ability to select export stream selection

* Fix for review comments

* Fix mypy

* Cleanup wording

web/public/locales/en/components/dialog.json

@@ -52,6 +52,15 @@
     "name": {
       "placeholder": "Name the Export"
     },
+    "stream": {
+      "label": "Quality",
+      "auto": "Auto",
+      "main": "Original",
+      "sub": "Low",
+      "autoDesc": "Uses the main stream and falls back to the lower quality sub stream where main is not available.",
+      "mainDesc": "Exports only the original quality main stream. Time ranges where the main stream is not available will be missing.",
+      "subDesc": "Exports only the lower quality sub stream. Time ranges where the sub stream is not available will be missing."
+    },
     "case": {
       "newCaseOption": "Create new case",
       "newCaseNamePlaceholder": "New case name",

web/public/locales/en/views/exports.json

@@ -63,6 +63,7 @@
     "copying": "Copying",
     "encoding": "Encoding",
     "encodingRetry": "Encoding (retry)",
+    "merging": "Merging",
     "finalizing": "Finalizing"
   },
   "caseView": {