deploy manifest errs when give a directory containing a manifest

从 rsconnect/main.py 中的 deploy_manifest() 开始，然后跟踪 rsconnect/bundle.py 中的 default_title_from_manifest() 和 read_manifest_file()。比较 manifest 验证后 file 和 file_name 的使用方式，并确认 rsconnect deploy manifest model 和直接的 manifest 路径都能在不出现目录错误的情况下完成。

The help for deploy manifest reads:

Usage: rsconnect deploy manifest [OPTIONS] FILE

  Deploy content to Posit Connect, Posit Cloud, or shinyapps.io using an
  existing manifest.json file.  The specified file must either be named
  "manifest.json" or refer to a directory that contains a file named
  "manifest.json".

However, when providing a directory that contains a manifest.json, an error results.

Traceback (most recent call last):
  File "BASE_DIR/env/lib/python3.11/site-packages/rsconnect/main.py", line 108, in wrapper
    result = func(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^
  File "BASE_DIR/env/lib/python3.11/site-packages/click/decorators.py", line 33, in new_func
    return f(get_current_context(), *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "BASE_DIR/env/lib/python3.11/site-packages/rsconnect/main.py", line 1119, in deploy_manifest
    kwargs["title"] = title or default_title_from_manifest(file)
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "BASE_DIR/env/lib/python3.11/site-packages/rsconnect/bundle.py", line 744, in default_title_from_manifest
    source_manifest, _ = read_manifest_file(file)
                         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "BASE_DIR/env/lib/python3.11/site-packages/rsconnect/bundle.py", line 757, in read_manifest_file
    with open(manifest_path, "rb") as f:
         ^^^^^^^^^^^^^^^^^^^^^^^^^
IsADirectoryError: [Errno 21] Is a directory: 'model'
Internal error: [Errno 21] Is a directory: 'model'

Providing the path to the manifest.json works.

# error
rsconnect deploy manifest model
# no error
rsconnect deploy manifest model/manifest.json

Using rsconnect-python 1.23.0.

The manifest is correctly identified:

rsconnect.bundle.validate_manifest_file("model")
#> 'model/manifest.json'

However, in deploy_manifest(), we rewrite the incoming file to file_name but do not consistently use that variable.

https://github.com/rstudio/rsconnect-python/blob/74b7f6899206ff754e29ad282c3dc725ab4e186b/rsconnect/main.py#L1146-L1179