refactor: create cost-insights-common isomorphic package

This moves most of the cost-insights API types into a separate
isomorphic @backstage/plugin-cost-insights-common package. This will
allow these types to be used by a a cost-insights backend or other
product specific modules.

Signed-off-by: Andrew Thauer <athauer@wealthsimple.com>

plugins/cost-insights-common/package.json

@@ -0,0 +1,42 @@
+{
+  "name": "@backstage/plugin-cost-insights-common",
+  "description": "Common functionalities for the cost-insights plugin",
+  "version": "0.0.1",
+  "main": "src/index.ts",
+  "types": "src/index.ts",
+  "license": "Apache-2.0",
+  "private": false,
+  "publishConfig": {
+    "access": "public",
+    "main": "dist/index.cjs.js",
+    "module": "dist/index.esm.js",
+    "types": "dist/index.d.ts"
+  },
+  "backstage": {
+    "role": "common-library"
+  },
+  "homepage": "https://backstage.io",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/backstage/backstage",
+    "directory": "plugins/cost-insights-common"
+  },
+  "keywords": [
+    "backstage"
+  ],
+  "scripts": {
+    "build": "backstage-cli package build",
+    "lint": "backstage-cli package lint",
+    "test": "backstage-cli package test",
+    "prepack": "backstage-cli package prepack",
+    "postpack": "backstage-cli package postpack",
+    "clean": "backstage-cli package clean"
+  },
+  "dependencies": {},
+  "devDependencies": {
+    "@backstage/cli": "^0.18.0-next.1"
+  },
+  "files": [
+    "dist"
+  ]
+}