Add script to keep .editorconfig in sync with .gitattributes

Add script to keep .editorconfig in sync with .gitattributes

Our repo already contained an .editorconfig file, but it was not kept
up to date with .gitattributes.  This adds a script that keeps these
files in sync.  A big advantage of the editorconfig file is that it
many editors/IDEs get automatically configured to trim trailing
newlines and add a final newline on save, while .gitattributes only
complains about these problems instead of automatically fixing them.

This also adds rules to .gitattributes for Python files as well as for
C files in pg_bsd_indent directory (which have a different tab_width
than most C files due to being vendored in).

Author: Jelte Fennema-Nio <github-tech@jeltef.nl>
Discussion: https://www.postgresql.org/message-id/flat/CAGECzQQGzbroAXi+Yicp3HvcCo4=g84kaOgjuvQ5MW9F0ubOGg@mail.gmail.com