rpm: Extend spec to support aarch64 and more

Refactoring and features in this patch:

- Add support for aarch64 build
- Add offline build configuration using vendored crates
- Add script to generate vendored sources
- Fix openssl-sys dependency

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

.gitignore

@@ -4,3 +4,4 @@
 **/*.rs.bk
 **/Cargo.lock
 **/rusty-tags.vi
+/rpm/SOURCES