refactor: separate deployer into serval api and implement query and scale

[shawnh2]

related to #160

in the following PR, the pkg/cmd, pkg/deployer, pkg/connector shall be removed or rewrote.

[codecov-commenter]

Codecov Report

Attention: 193 lines in your changes are missing coverage. Please review.

Comparison is base (c64a3c2) 35.80% compared to head (ab1d381) 34.29%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #165      +/-   ##
===========================================
- Coverage    35.80%   34.29%   -1.51%     
===========================================
  Files           12       16       +4     
  Lines         1430     1522      +92     
===========================================
+ Hits           512      522      +10     
- Misses         814      893      +79     
- Partials       104      107       +3     

Files	Coverage Δ
pkg/cluster/baremetal/validate.go	84.21% <84.21%> (ø)
pkg/cluster/baremetal/not_implemented.go	0.00% <0.00%> (ø)
pkg/cluster/baremetal/config.go	0.00% <0.00%> (ø)
pkg/cluster/baremetal/cluster.go	0.00% <0.00%> (ø)
pkg/cluster/baremetal/get.go	12.87% <12.87%> (ø)

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[zyy17]

What a big PR #_#, let me slow down and have a look.

[zyy17]

I have another abstraction design as the following structs that can be more clean:

type Cluster struct { ... }

type ClusterOperation interface {
    Create(ctx context.Context, name string, options *CreateOptions) error
    Get(ctx context.Context, name string, options *GetOptions) (*Cluster, error)
    List(ctx context.Context, options *ListOptions) ([]*Cluster, error)
    Update(ctx context.Context, options *UpdateOptions)
    Connect(ctx context.Context, options *ConnectOptions)
}

We can implement the K8s and bare-metal clusteroption and provide the factory method. For K8s mode, the creation of an etcd cluster and operator can be hidden in Create().

For this PR, IMHO:

1. pkg/api: I think it's better to maintain in pkg/cluster. api is more like the interface for cli users. But in this scenario, it's the apis for internal usage.
2. pkg/api/scale and pkg/api/query: maybe the two apis are too small, and it's unnecessary to split them from the parent interface. Keep in one interface will be clean;

[shawnh2]

I have another abstraction design as the following structs that can be more clean:

type Cluster struct { ... }

type ClusterOperation interface {
    Create(ctx context.Context, name string, options *CreateOptions) error
    Get(ctx context.Context, name string, options *GetOptions) (*Cluster, error)
    List(ctx context.Context, options *ListOptions) ([]*Cluster, error)
    Update(ctx context.Context, options *UpdateOptions)
    Connect(ctx context.Context, options *ConnectOptions)
}

We can implement the K8s and bare-metal clusteroption and provide the factory method. For K8s mode, the creation of an etcd cluster and operator can be hidden in Create().

For this PR, IMHO:

1. pkg/api: I think it's better to maintain in pkg/cluster. api is more like the interface for cli users. But in this scenario, it's the apis for internal usage.
2. pkg/api/scale and pkg/api/query: maybe the two apis are too small, and it's unnecessary to split them from the parent interface. Keep in one interface will be clean;

great idea, made some changes, PTAL @zyy17

[zyy17]

LGTM