Add githooks to manage commit DCO sign-off

[mentonin]

Adds a local commit-msg git-hook to check for commit messages without the DCO "Signed-off-by:" trailer.

Closes: #1922
Related: #1930, #1931

Caveats

• Does not check that the DCO is valid (same email as committer)
• Only works as a dev convenience. Actual repo verification should be enabled via GH settings/CI (see Automate rejecting commits without a DCO sign-off #1930)

[bhcopeland]

Looks good thanks for this. To me but I'd probably stay away from "auto filling DCO" and leave that to user, but block the pipeline. Having CI adjust the commit + autofill seems risky to me.

[mentonin]

The way I set this up, it has 2 hooks:

1. The prepare-commit-msg hook adds the sign-off if an editor will open later to edit the commit message (i.e. it never changes your commit silently).

2. The commit-msg hook checks if there is a DCO and blocks the commit otherwise, with an error message suggesting --signed|-s usage

The CI never adjusts the commit, unless I misunderstand something about how GH handles git hooks. If you think the prepare-commit-msg hook is still too risky, which would you like best:

1. Remove it completely
2. Keep it, but move documentation out of general setup and better explain the consequences
3. Comment out the auto-added sign-off, adding convenience but requiring a manual action
4. Add comments around the line reminding the user what the DCO is, why the comment shows up, or to use --signed|-s

[bhcopeland]

Apologies I read it too quick, yes this is a local git hook. I'd drop this though still and go for 1. Just keep the ci check in place (and leave users to themselves).

[bhcopeland]

You want to remove the trailing $1 here. This will read it from stdin and exit 0 if it exists.

[alanpeixinho]

I think I am with @bhcopeland, might be safer if we just use the pre commit check for DCO, and leave the user to add it by themselves.
I am not sure if we have permissions to add check on CI as well, but if we do, might be a good idea.

[mentonin]

Removed the prepare-commit-msg hook and fixed code, ready for another review

[bhcopeland]

LGTM :)

[alanpeixinho]

LGTM