feat: store `packageManager` property also inside the lock file

Our current flow:
We use docker + pnpm fetch

COPY --chown=node:node pnpm-*.yaml .npmrc ./
RUN npm install -g pnpm@^8 # curernt usage without corepack
# RUN corepack enable #  <= but we want this one
RUN --mount=type=cache,id=pnpm,target=/pnpm/store pnpm fetch --loglevel=warn --ignore-scripts

This means we don't cache the package.json file before the pnpm fetch execution.
This allows us to worry about package.json changes.
But corepack will always install the latest version of pnpm instead of a specific one.

If store the packageManager property in a lock file, this will solve the problem.

Start by tracing the Docker flow using pnpm fetch and how package.json, pnpm-*.yaml, and .npmrc are handled before fetching. Determine how the lock file is read or generated, then ensure it preserves the packageManager property so corepack can select the pinned pnpm version without copying package.json first.