Skip customize files + set workdir

[msanterre]

Skip the rendering of kustomize files, and adds the ability for users to set the work directory of the app.

Testing on chime-cd:
go run main.go hashing.go --workdir ../chime-cd/ -root=bootstrap/child-applications-us-east-1/devex-develop2 -output=zz.auto-generated/root-use1-devex-develop2/ -hash-store=json -ignore-suffix=-console -skip-render-key=appTag -ignore-value-file=overrides/apptags.

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[Nicolas-Richard]

lgtm

[d1egoaz]

Just a couple of comments.

We really need to add unit tests to this.
Probably in the future, we need to keep working on https://github.com/1debit/mani-diffy/pull/9/files to make writing unit tests easier.