feat: enforce using lockfile in p3-convert

[web-padawan]

Description

Connected to https://github.com/vaadin/components-team-tasks/issues/602

1. From now on, we assume that individual repositories keep package-lock.json in version control
2. Added logic to handle package-lock-p3.json renaming (the file needs to be created manually)

To use this feature, the following changes are needed:

1. Use this branch: https://github.com/vaadin/vaadin-component-dev-dependencies/tree/feat/lockfile
2. Remove yarn install --flat from the GitHub Actions P3 workflows due to launchpad issue.

Type of change

• Feature