Enable BLS portable feature on all CI tests (#4868)

## Issue Addressed

Addresses the recent CI failures caused by caching `blst` for the wrong CPU type. 

## Proposed Changes

- Use `FEATURES: jemalloc,portable` when building Lighthouse & `lcli` in tests
- Add a new `TEST_FEATURES` and set to `portable` for all CI test jobs.
- Updated Makefiles to read the `TEST_FEATURES` environment variable, and default to none.

testing/state_transition_vectors/Makefile

@@ -2,7 +2,7 @@ produce-vectors:
 	cargo run --release
 
 test:
-	cargo test --release
+	cargo test --release --features "$(TEST_FEATURES)"
 
 clean:
 	rm -r vectors/