fix(merge-from-scope), do not throw an error about missing artifacts when merging main to a lane

[davidfirst]

Previously, collectVersionsObjects had a bug, ignoreMissingLocalArtifacts didn't do anything, even when it was false, it was still ignoring local artifacts because locallyChangedHashes.includes(versionObject.hash.toString()) always returned false. The versionObject.hash.toString() printed the hash method instead of the hash content. It's fixed to be versionObject.hash().toString() to make it work.
Because of the that bug, #7119 was adding new flag ignoreMissingExternalArtifacts unnecessarily. It assumed that an error wasn't thrown because it was external which wasn't correct. In this PR this flag has removed.
In addition to this, when merging from scope and merging main to a lane, we can skip the import of the artifacts because once the user asks for the artifacts we retrieve it from main if not found in the lane.

One last thing, because until now ignoreMissingLocalArtifacts practically did nothing, I'm afraid that after this fix it'll throw errors unnecessarily, so I made the default to not throw when missing. We didn't get any complain about missing artifacts in the remote scopes, so it should be fine.
This flag was renamed to throwForMissingLocalArtifacts for clarity. The only place we throw is when merging-from-scope and the source is a lane, not main.