Add .editorconfig

FreeBSD developers use different text editors or sometimes use GUI
editors such as VSCode or Zed on different platforms for convinence.
However, there is lack of unified config for those editors to follow
style(9) including indent rules.

Although most "modern" editors support .editorconfig out of box, basic
editors such as vim needs a plugin for autoloading .editorconfig file.

Sponsored by:	The FreeBSD Foundation

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/2024

.editorconfig

@@ -0,0 +1,23 @@
+[{contrib/**,**/contrib/**,kerberos5/**,krb5/**,crypto/**,sys/crypto/openssl/**}]
+ignore = true
+
+[{*.{awk,c,dts,dtsi,dtso,h,mk,s,S},Makefile,Makefile.*}]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+indent_style = tab
+indent_size = 8
+
+[*.py]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+indent_style = space
+indent_size = 4
+
+[*.{yaml,yml}]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+indent_style = space
+indent_size = 2