commit:validate command

[matthiaz]

We occasionally get customers that destroy their data by renaming a container. It's documented, but it gets missed.

This PR adds a new platform commit:validate method that can check the commit against a few common mistakes that users do.

platform get will now create a pre-commit hook to launch that validate command.
This will protect the user from mistakes, before they push it to us.

Currently, this pre-commit hook warns when it detects:

• Downgrades of services (mysql, mongodb...) (also warns on upgrades since a downgrade usually follows an upgrade that went bad)
• Changing the name of an application container (which would destroy mount data)
• Changing the name of a service container container (which would destroy database data)
• Committing files larger than 1MB
• Warns of going over plan disk usage
• Checks for common mistakes in the build hook that cause stuck builds (e.g npm run serve)

It will not block the commit, you will get asked if you want to continue. And you can also disable each check individually using git config

To stop platform get from creating the hooks, you can do platform get --no-create-hooks (handy for scripts).

[matthiaz]

@pjcdawkins do you need further input from me on this?
I'm looking back into this and it still has its uses.