Reexport ink_metadata in transcoder crate

[0xLucca]

Summary

Closes #1521

• [n] y/n | Does it introduce breaking changes?
• [n] y/n | Is it dependent on the specific version of ink or pallet-contracts?

Description

This PR solves issue #1521

Checklist before requesting a review

• My code follows the style guidelines of this project
• I have added an entry to CHANGELOG.md
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• Any dependent changes have been merged and published in downstream modules

[cla-bot-2021]

User @0xLucca, please sign the CLA here.

[cmichi]

@0xLucca Can you fix the CI? It should be a simple cargo fmt.

[ascjones]

Please provide a more descriptive title to the PR

[0xLucca]

I've just updated the PR title