Service/Storage Config Support

[Xuanwo]

We have a internal struct now:

type pairServiceNew struct {
	pairs []Pair

	// Required pairs
	HasCredential bool
	Credential    string
	// Optional pairs
	HasDefaultServicePairs bool
	DefaultServicePairs    DefaultServicePairs
	HasDisable100Continue  bool
	Disable100Continue     bool
	HasEndpoint            bool
	Endpoint               string
	HasForcePathStyle      bool
	ForcePathStyle         bool
	HasHTTPClientOptions   bool
	HTTPClientOptions      *httpclient.Options
	HasServiceFeatures     bool
	ServiceFeatures        ServiceFeatures
	HasUseAccelerate       bool
	UseAccelerate          bool
	HasUseArnRegion        bool
	UseArnRegion           bool
}

Maybe we can export this struct as StorageConfig and implement following methods for it:

• FromPairs(ps Pair...) -> parse from pairs, just like NewStorage(ps Pair...)
• FromString(conn string) -> parse from connection string, just like NewStorageFromString(conn string)
• Add json/toml/yaml tags (so that user can unmarshal it directly)

We need the following changes:

• Add new function like NewStorageFromConfig(cfg StorageConfig)?
• field HasUseAccelerate needs to be converted to internal -> hasUseAccelerate?
• struct should be renamed to StorageConfig?
• Extact new interface including FromPairs, FromString so that we can register it?
• Can we keep all public API compatible

[Xuanwo]

Moved to https://forum.beyondstorage.io/t/idea-about-servicer-storager-init-logic/185