Group metadata doesn't get serialized

[robertbindar]

As @snagles reported, the group metadata seems to be written correctly, but it's empty when you try to read it. I managed to reproduce it locally by opening a TileDB Cloud group, then created a test for it by serializing-deserializing a group with metadata locally. The serialization code is calling Group::metadata() to get the md object, but the Metadata content is not brought up from disk, so the group looks like it has no metadata. Group::load_metadata needs to be called to make sure we serialize a synced version of Metadata.

This bug most probably can be reproduced in 2.9 as well as the code looks identical in those parts.

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TYPE: BUG DESC: Group metadata doesn't get serialized

[ihnorton]

I believe Cloud team has worked around this issue for now, converting to draft pending further discussion with @Shelnutt2.