Add dynamic types support

[smiasojed]

Summary

Related #1168

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

Description

Remove the need for compile-time node metadata stored in extrinsics/src/runtime_api/metadata.scale, and update the subxt setup to utilize dynamic values instead of static.
Note that the metadata is retained solely for testing purposes.

Checklist before requesting a review

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

[ascjones]

Could we put all type definitions and constructors for extrinsics and storage keys etc. together in a single module?

The raw subxt stuff is better encapsulated, and it will be easier once we need to have multiple definitions for different versions.