script: Add ability to insert copyright to *.sh
script: Add empty line after C++ copyright
script: Update EXLUDE list in copyright_header.py
This is a backport of core#17691 [1/2]
https://github.com/bitcoin/bitcoin/pull/17691/commits/071f2fc204f542c5a287ca8835115a2ee0bf2f50
https://github.com/bitcoin/bitcoin/pull/17691/commits/1998152f15fd2b0e83f5068c375a34feaf73db8c
https://github.com/bitcoin/bitcoin/pull/17691/commits/6fde9d5e47fc9a1042b3fb68031eab5bf55e508d