build: add Makefile and GHA workflow to ensure dist folders are up-to-date

[xnyo]

Makes the following changes:

• Adds a Makefile for generating and checking drifts in the dist files for bundled JS actions (JS actions with dist folder built via @vercel/ncc, currently only e2e-versions).
• Adds a GHA workflow to ensure that dist folders are up-to-date when there are code changes. Uses the Makefile under the hood

In order for bundled JS actions to be compatible with this system, they must have:

• a .nvmrc pinning an exact Node version (e.g. 24.11.0)
• exact, caret-free versions for the inlined runtime deps and @vercel/ncc in package.json (e.g. "@actions/core": "3.0.1", not "^3.0.1")
• a committed package-lock.json, always installed with 'npm ci'
• a 'bundle' script in package.json that writes to dist/

These required steps are also checked by the dedicated make check-setup target, and the same message is also printed in CI when an action doesn't have the correct setup

Example failure: https://github.com/grafana/plugin-actions/actions/runs/27817139800/job/82321092585?pr=250