crate_universe: Generate shallow_since

I'd like to propose the crate_universe generator include `shallow_since` within the lock file. As it stands, transitive Cargo dependencies from git don't include `shallow_since` which leads to lots of log spam like:

```sh
(16:06:54) DEBUG: Rule 'crate_index__-0.1.0' indicated that a canonical reproducible form can be obtained by modifying arguments shallow_since = "1643038190 +0000"
(16:06:54) DEBUG: Repository crate_index__-0.1.0 instantiated at:
/Users/thomas/code//WORKSPACE:198:19: in
/private/var/tmp/_bazel_thomas/796dd52d4d981101108548a9446ddca6/external/crate_index/defs.bzl:1321:10: in crate_repositories
/private/var/tmp/_bazel_thomas/796dd52d4d981101108548a9446ddca6/external/bazel_tools/tools/build_defs/repo/utils.bzl:233:18: in maybe
Repository rule new_git_repository defined at:
/private/var/tmp/_bazel_thomas/796dd52d4d981101108548a9446ddca6/external/bazel_tools/tools/build_defs/repo/git.bzl:186:37: in
```

Consequently, the `crates_repository` rule then becomes filled with needless annotations for `shallow_since`.