import: Added --json-progress

Already supported --json, but not that.

Also checked all other commands that only support --json, and the only
other one that does transfers is fsck (--from), which it did not seem worth
adding --json-progress to really.

CHANGELOG

@@ -1,6 +1,7 @@
 git-annex (8.20200523) UNRELEASED; urgency=medium
 
   * export: Added options for json output.
+  * import: Added --json-progress.
   * addurl: Make --preserve-filename also apply when eg a torrent contains
     multiple files.
 

Command/Import.hs

@@ -38,7 +38,7 @@ import Control.Concurrent.STM
 
 cmd :: Command
 cmd = notBareRepo $
-	withGlobalOptions [jobsOption, jsonOptions, fileMatchingOptions] $
+	withGlobalOptions [jobsOption, jsonOptions, jsonProgressOption, fileMatchingOptions] $
 		command "import" SectionCommon 
 			"add a tree of files to the repository"
 			(paramPaths ++ "|BRANCH[:SUBDIR]")

doc/git-annex-import.mdwn

@@ -171,6 +171,10 @@ and `--reinject-duplicates` documentation below.
   Enable JSON output. This is intended to be parsed by programs that use
   git-annex. Each line of output is a JSON object.
 
+* `--json-progress`
+
+  Include progress objects in JSON output.
+
 * `--json-error-messages`
 
   Messages that would normally be output to standard error are included in