feat(export): export defaultMetadataStorage

[thongxuan]

Description

This PR exports default metadata storage which allow picking & subclassing class decorated with class-transfomer.

Checklist

• the pull request title describes what this PR does (not a vague title like Update index.md)
• the pull request targets the default branch of the repository (develop)
• the code follows the established code style of the repository
  • npm run prettier:check passes
  • npm run lint:check passes
• tests are added for the changes I made (if any source code was modified)
• documentation added or updated
• I have run the project locally and verified that there are no errors

Fixes

fixes #[issue number], fixes #[issue number]

[diffy0712]

Hello @thongxuan,

did you create any issue (or could you find any open issue) for this pr detailing the need for this? If not, could you please describe when would this export be used?

Thank you

[scottwday]

This is related to this issue: #815
This is needed for #563