#326: Backport update to cobra and UX improvements

[tashima42]

Closes: #326

What changed

• Makes the flag owner optional
• Updates the backport command to use cobra
• Adds dry run
• Adds logs
• Updates running commands to use the ecm exec package
• Changes the workflow to create issues right after pushing branches, to avoid duplicating issues due to git errors on multiple runs
• Improves documentation on backport and k3s release

How to test

• Fork k3s
• Create an issue on your fork

cd k3s
export GITHUB_TOKEN={YOUR_GITHUB_TOKEN}
cmd/backport/bin/backport-darwin-arm64 -r k3s -i {ISSUE_ID} -o {YOUR_USERNAME} -u {YOUR_USERNAME} -b "release-1.26" -c cd700d9a444df8f03b8ce88cb90261ed1bc49f27 -n