feat: add the unified metadata manager

[zyy17]

What's changed

The pkg/metadata is a simple implementation of a metadata manager that manages the artifacts file path.

Moreover, the manager should also manage the runtime metadata of different deployments. We can improve it in the next development(cc @shawnh2).

Related issue: #150.

[codecov-commenter]

Codecov Report

Attention: 39 lines in your changes are missing coverage. Please review.

Comparison is base (dda81be) 34.54% compared to head (8c00048) 35.17%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #158      +/-   ##
===========================================
+ Coverage    34.54%   35.17%   +0.63%     
===========================================
  Files           10       11       +1     
  Lines         1297     1359      +62     
===========================================
+ Hits           448      478      +30     
- Misses         760      787      +27     
- Partials        89       94       +5     

Files	Coverage Δ
pkg/cmd/gtctl/cluster/create/create.go	0.00% <0.00%> (ø)
pkg/artifacts/manager.go	56.42% <20.00%> (-0.77%)	⬇️
pkg/metadata/manager.go	85.29% <85.29%> (ø)
pkg/helm/helm.go	58.47% <50.00%> (-4.03%)	⬇️
pkg/deployer/baremetal/deployer.go	30.42% <19.23%> (-0.99%)	⬇️

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