Add startup lifecycle hook (#1531)

* checkpoint

* Finish missing tests; remove redundant v1 tests

* Fix linter error

* Fix import error

* Add changelog; fix exports of v2/core

Author: inlined

CHANGELOG.md

@@ -0,0 +1 @@
+Add onInit callback function for global variable initialization (#1531)

package.json

@@ -110,6 +110,9 @@
       "v2": [
         "lib/v2"
       ],
+      "v2/core": [
+        "lib/v2/core"
+      ],
       "v2/alerts": [
         "lib/v2/providers/alerts"
       ],
@@ -250,4 +253,4 @@
   "engines": {
     "node": ">=14.10.0"
   }
-}
+}