Add default value for target in prune cli (#1253)

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### Summary

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Resolves #111 and #222.
Depends on #1000 (for series of dependent commits).

This PR introduces this capability to make the project better in this
and that.

- Added this feature
- Removed that feature
- Fixed the problem #1234
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- Fix prune cli #1225 
- Remove unnecessary line for dataset saving

### How to test
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not fully covered by unit tests or manual testing can be complicated.
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- Use existed cli test

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- [ ] I have added integration tests to cover my changes.​
- [X] I have added the description of my changes into
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[documentation](https://github.com/openvinotoolkit/datumaro/tree/develop/docs)
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CHANGELOG.md

@@ -59,6 +59,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   (<https://github.com/openvinotoolkit/datumaro/pull/1244>)
 - Fix input tensor shape in model interpreter for OpenVINO 2023.3
   (<https://github.com/openvinotoolkit/datumaro/pull/1251>)
+- Add default value for target in prune cli
+  (<https://github.com/openvinotoolkit/datumaro/pull/1253>)
 
 ## 16/11/2023 - Release 1.5.1
 ### Enhancements

src/datumaro/cli/commands/prune.py

@@ -4,6 +4,7 @@
 
 import argparse
 import logging as log
+import os.path as osp
 
 from datumaro.components.algorithms.hash_key_inference.prune import Prune
 from datumaro.components.errors import ProjectNotFoundError
@@ -45,7 +46,13 @@ def build_parser(parser_ctor=argparse.ArgumentParser):
         formatter_class=MultilineFormatter,
     )
 
-    parser.add_argument("target", nargs="?", help="Target dataset revpath (default: project)")
+    parser.add_argument(
+        "target",
+        nargs="?",
+        default="project",
+        metavar="revpath",
+        help="Target dataset revpath (default: project)",
+    )
     parser.add_argument("-m", "--method", dest="method", help="Method to apply to the dataset")
     parser.add_argument(
         "-r", "--ratio", type=float, dest="ratio", help="How much to remain dataset after pruning"
@@ -110,12 +117,12 @@ def prune_command(args):
     source_dataset = [parse_full_revpath(target, project)[0] for target in targets][0]
 
     prune = Prune(source_dataset, cluster_method=args.method, hash_type=args.hash_type)
-
-    source_dataset.save(source_dataset.data_path, save_media=True, save_hashkey_meta=True)
-
     result = prune.get_pruned(args.ratio)
 
     dst_dir = args.dst_dir or source_dataset.data_path
+    dst_dir = (
+        dst_dir if dst_dir else osp.join(args.project_dir, list(project.working_tree.sources)[0])
+    )
     result.save(dst_dir, save_media=True)
 
     log.info("Results have been saved to '%s'" % dst_dir)