Use studio-plugin version in package.json instead of wildcard (#355)

In npm workspaces, you can use `*` to point to a local dependency (i.e.
another package), which is how we add `studio-plugin` as a dependency of
`studio`. This dependency is preserved as a symlink in the root
`package-lock.json`. Since the dependency version of `studio-plugin` in
the `studio` `package.json` was `*`, there was not a concrete version of
`studio-plugin` specified, so users had to explicitly install `studio`
and `studio-plugin`. This PR finds that we can still specify a version
of `studio-plugin` in the `studio` `package.json` and still preserve the
symlink for local development.

J-SLAP-2895
TEST=manual

packages/studio/package.json

@@ -20,7 +20,7 @@
     "@minoru/react-dnd-treeview": "^3.4.1",
     "@restart/ui": "^1.5.2",
     "@vitejs/plugin-react": "^4.0.4",
-    "@yext/studio-plugin": "*",
+    "@yext/studio-plugin": "0.20.0",
     "autoprefixer": "^10.4.14",
     "cac": "^6.7.14",
     "classnames": "^2.3.2",