Add prepublish hook to unpin deps only for published version

[ecraig12345]

Since lage is bundled, dependencies should be pinned to ensure that direct dep updates are explicit, not implicit due to lock file changes. (The implicit update issue unfortunately still exists for sub-dependencies, but pinning direct deps reduces it.) However, the pinned deps are unfortunate for anyone consuming the sub-packages directly.

This PR adds a beachball pre-publish hook to unpin the deps just before publishing.

Test with: yarn release --no-push -n faketoken

[ecraig12345]

Pinning was added in #712, so presumably the implicit dep update bug that prompted pinning happened in Dec. 2023 or earlier (and Feb. 2023 or later, after bundled lage v2 was promoted to latest in #572), but I can't find anything mentioning it in the commit history or issues...