This largely copies over Spicy's `.clang-format` configuration file. The
one place where we deviate is header include order since Zeek depends on
headers being included in a certain order.
- Be explicit about setting the copied flag in session::Key. Coverity seems
confused about when that flag is set if it gets set by default
initialization. This should fix 1452757 and 1452759.
- Explicitly copy the fields in ConnKey instead of using memcpy. Fixes
1452758.