Add TableMetadataBuilder::assign_current_snapshot_id

[SergeiPatiakin]

TableMetadataBuilder::from_table_creation initializes current_snapshot_id to None. This PR adds a builder method that allows different values.

[c-thiel]

Thanks @SergeiPatiakin for your PR!

Assigning the current snapshot id is a bit more complex than what you have in your PR.
Here is the extract from the spec: https://iceberg.apache.org/spec/#table-metadata-fields
current-snapshot-id: ID of the current table snapshot; must be the same as the current ID of the main branch in refs.

The logic you are looking for is already implemented in #587 which is currently under review. I am optimistic that we can include it in the next release.

Could you check if #587 serves your usecase? Check the set_ref method:
https://github.com/apache/iceberg-rust/pull/587/files#diff-464f76c3b76da41490c8fac47aa4aef4287fffdd0ca0766ae431c4829d59aa30R462

If so, would it be OK to close this PR?

[SergeiPatiakin]

Thanks! You are right, I think I'll be able to use TableMetadataBuilder::set_ref from #587 . Closing this PR