Investigate adding type to StoragePlaceholder

[igamigo]

On #1015, we add StoragePlaceholder for defining template values in the storage layout of AccountComponentMetadata. On instantiation, these are meant to be replaced by one StorageValue per placeholder.
The placeholders could take the value of a felt, word, or map, so one potential improvement to the workflow could be to make StoragePlaceholder carry the type of the expected value. This could help the user query which type of values each key requires, so that they could check beforehand that all are correct before actually instantiating.
When deserializing a toml component, the type could be picked up according to the place the placeholder is located at.

[bobbinth]

This is being addressed in #1074, right?

[igamigo]

Sorry I missed the comment before. Yes, this was closed by #1074