fix Docker build (#553)

We're a bit behind on pnpm versions and this causes issues with newer
node installs and corepack. The issue is related to verifying the PNPM
tarball signature, and it's failing because the signature in the TUF
metadata cannot be validated—likely due to a key mismatch or
expired/incomplete keyring used by Corepack:

```
Internal Error: Cannot find matching keyid: {"signatures":[{"sig":"MEUCIQDH6Kte1awtFvRUVsKWHtRaKuryH/0lm0Wswd29C+NdWAIgMxcudJ1cOlbnCh3oiFLkrQLua0vp6H+mGvycpY4TzxM=","keyid":"SHA256:DhQ8wR5APBvFHLF/+Tc+AYvPOdTpcIDqOhxsBHRwC7U"}],"keys":[{"expires":null,"keyid":"SHA256:jl3bwswu80PjjokCgh0o2w5c2U4LhQAE57gj9cz1kzA","keytype":"ecdsa-sha2-nistp256"
```

To work arround this I'm installing a pinned version of pnpm through
corepack:
```
RUN corepack enable && corepack prepare [email protected] --activate
```

And removed the please use pnpm check script, its no longer needed.
People can figure it out or they should read the readme.

Author: jfboeve

Dockerfile

@@ -9,7 +9,7 @@ COPY .npmrc .npmrc
 COPY package.json package.json
 
 # Install PNPM
-RUN corepack prepare && corepack enable
+RUN corepack enable && corepack prepare [email protected] --activate
 
 # Get pnpm to install the version of Node declared in .npmrc
 RUN pnpm exec ls

package.json

@@ -14,7 +14,6 @@
     "./inspector": "./dist/exports/inspector.js"
   },
   "scripts": {
-    "preinstall": "node scripts/please-use-pnpm.js",
     "start": "cd examples && pnpm start",
     "start:prod": "cd examples && pnpm start:prod",
     "build": "tsc --build",