Support for content-level compression (#1076)

* cli: added a flag to create repository with v2 index features

* content: plumb through compression.ID parameter to content.Manager.WriteContent()

* content: expose content.Manager.SupportsContentCompression

This allows object manager to decide whether to create compressed object
or let the content manager do it.

* object: if compression is requested and the repo supports it, pass compression ID to the content manager

* cli: show compression status in 'repository status'

* cli: output compression information in 'content list' and 'content stats'

* content: compression and decompression support

* content: unit tests for compression

* object: compression tests

* testing: added integration tests against v2 index

* testing: run all e2e tests with and without content-level compression

* htmlui: added UI for specifying index format on creation

* cli: additional tests for 'content ls' and 'content stats'

* applied pr suggestions

internal/serverapi/serverapi.go

@@ -18,14 +18,15 @@ import (
 
 // StatusResponse is the response of 'status' HTTP API command.
 type StatusResponse struct {
-	Connected    bool   `json:"connected"`
-	ConfigFile   string `json:"configFile,omitempty"`
-	Hash         string `json:"hash,omitempty"`
-	Encryption   string `json:"encryption,omitempty"`
-	Splitter     string `json:"splitter,omitempty"`
-	MaxPackSize  int    `json:"maxPackSize,omitempty"`
-	Storage      string `json:"storage,omitempty"`
-	APIServerURL string `json:"apiServerURL,omitempty"`
+	Connected                  bool   `json:"connected"`
+	ConfigFile                 string `json:"configFile,omitempty"`
+	Hash                       string `json:"hash,omitempty"`
+	Encryption                 string `json:"encryption,omitempty"`
+	Splitter                   string `json:"splitter,omitempty"`
+	MaxPackSize                int    `json:"maxPackSize,omitempty"`
+	Storage                    string `json:"storage,omitempty"`
+	APIServerURL               string `json:"apiServerURL,omitempty"`
+	SupportsContentCompression bool   `json:"supportsContentCompression"`
 
 	repo.ClientOptions
 }