Allow user of zero cli to overwrite destination files during create

[bmonkman]

Add an --overwrite argument to zero create to allow a user to overwrite any files that already exist when templating.
Some support for this already exists in the code, as we used to support this, but it will need to be tested. (see generate_modules.go)

[GrooveStomp]

First run with zero create, then record file modification times via: tree -D:
https://app.zenhub.com/files/203630543/91eeee62-354e-4fa0-ba98-81a1da23b89a/download

Second run with zero create --overwrite and file modification times recorded via: tree -D:
https://app.zenhub.com/files/203630543/6ac64bcd-693b-40d3-9e9a-baa04e562460/download

Diff of the file modification times via: diff log1.txt log2.txt --suppress-common-lines --suppress-blank-empty
https://app.zenhub.com/files/203630543/f622cb38-043d-4726-96db-fa08985bdbeb/download