rename field in `get_contract_metadata_result` into `value`

[roaminro]

Brief description

Rename the get_contract_metadata_result contract_metadata field into value to comply with other syscalls format.

Checklist

• [x] I have built this pull request locally
• [ ] I have ran the unit tests locally
• [x] I have manually tested this pull request
• [x] I have reviewed my pull request
• [ ] I have added any relevant tests

[roaminro]

@mvandeberg looks like a workflow failed, preventing the merge of the PR ;)