* Create CLI tool for slashing export
* Use SQLite as a DB instead of a KV-store
* Keeps v1 and v2 DBs around
* Uses the same schema as Lighthouse v1.1.0
* Passes all interchange tests + skeleton of finalization pruning
* Removes tests that would violate v5 / minimal slashing DB and MinSlot rules
* Migration tool added using low-watermark scheme for faster migration of large number of validators
* update test submodule [skip ci]
* rename the process_lfs script to setup_official_tests [skip ci]
* clarify that the existing LFS is for json files [skip ci]
* Update again to use download/unpack function library
* update the test downloading script [skip ci]
* Update EF fixtures with new test path
* fix symlink order
* Fix relative:absolute symlink issue
* add symlink existence check
* setup_official_tests.sh: refactoring