The previous python3 -c '...' approach broke when lambdas
contained single quotes (e.g. '"' + tag + '"'), causing
the bash string to terminate early and output literal text
instead of variable values.
Adds tag-keys input (comma-separated) to update arbitrary YAML keys
instead of just 'tag'. Handles unquoted values, quoted values, and
YAML anchors (e.g. rustImageTag: &rustImageTag "value").
Makes image-repository optional when using custom tag-keys.