Actually enforce dashboard schema on devenv (#53797)

* Relocate dashboards test so it runs

* Cover newer schema versions in stripnulls

* Strip nulls and remove iteration fields

* Fix fiscalYearStartMonth bounds

* Fix up and format dashboard schema

* Update thema, tidy Go dependencies

devenv/dev-dashboards/e2e-repeats/Repeating-a-panel-horizontally.json

@@ -25,7 +25,6 @@
   "fiscalYearStartMonth": 0,
   "graphTooltip": 0,
   "id": 95,
-  "iteration": 1652465568602,
   "links": [],
   "liveNow": false,
   "panels": [

devenv/dev-dashboards/e2e-repeats/Repeating-a-row-with-a-non-repeating-panel-and-horizontal-repeating-panel.json

@@ -25,7 +25,6 @@
   "fiscalYearStartMonth": 0,
   "graphTooltip": 0,
   "id": 85,
-  "iteration": 1652465607869,
   "links": [],
   "liveNow": false,
   "panels": [