conductor: run any script

[acpana]

Add the ability to run any script! on the branches.

Sometimes you just want to git reset HEAD^ --hard or make fmt or something else!

$ make build && ./bin/conductor runner --branch-repo=<REPO_PATH> --branch-conf=branches.yaml --logging-dir=./logs --command=-5 --script=script.sh

Went with -5 bc this is a bit of a footgun.

[google-oss-prow]

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[cheftako]

Especially for a foot gun like this you need to set up the logging.
close := setLoggingWriter(opts, branch)
defer close()

[cheftako]

Clearly need to fix the logging.
Other concerns

• Its a foot gun
• Having tested and working commands which have been through code review is safer on multiple fronts including security
• Your examples git reset HEAD^ --hard or make fmt are great but I would rather these are common shared and supported commands. Having them as scripts discourages sharing these solutions.