The unified metadata management

[zyy17]

Background

For different deployment modes, the gtctl needs to store the metadata in .gtctl, for example:

• The downloaded artifacts(I think we also need a unified artifacts manager The unified artifacts manager #151);
• The deployment metadata (like dirs or files etc)

We should design a unified metadata management to handle the above scenarios, or similar logic will spread everywhere.

[shawnh2]

right now we have some basic implementation of these managers:

• artifacts manager feat: add the unified artifacts manager #157
• metadata manager feat: add the unified metadata manager #158 refactor: add runtime manager for bare-metal cluster #169

so close this one in favor of these PRs. will raise a new issue if we encounter some new cases.