`python3 setup.py sdist` does not create an installable archive

# Steps to reproduce

```
curl -fLO https://github.com/confluentinc/confluent-docker-utils/archive/refs/tags/v0.0.78.tar.gz
tar xzf v0.0.78.tar.gz
cd confluent-docker-utils-0.0.78/
python3 setup.py sdist
pip3 install dist/confluent-docker-utils-0.0.78.tar.gz
```

# Expected result

All requirements are downloaded, and the package installs

# Actual behavior
```
Processing ./dist/confluent-docker-utils-0.0.78.tar.gz
ERROR: Command errored out with exit status 1:
command: /usr/bin/python3.9 -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-req-build-wul03re5/setup.py'"'"'; __file__='"'"'/tmp/pip-req-build-wul03re5/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-pip-egg-info-05dl5x3l
cwd: /tmp/pip-req-build-wul03re5/
Complete output (5 lines):
Traceback (most recent call last):
File "", line 1, in
File "/tmp/pip-req-build-wul03re5/setup.py", line 15, in
install_requires=open('requirements.txt').read(),
FileNotFoundError: [Errno 2] No such file or directory: 'requirements.txt'
----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.
```

# Miscellany

`python3 setup.py install` DOES claim to work, but running `cub` and `dub` afterward yields:
```
Traceback (most recent call last):
File "/usr/local/bin/cub", line 33, in
sys.exit(load_entry_point('confluent-docker-utils==0.0.78', 'console_scripts', 'cub')())
File "/usr/local/bin/cub", line 25, in importlib_load_entry_point
return next(matches).load()
File "/usr/lib64/python3.9/importlib/metadata.py", line 86, in load
module = import_module(match.group('module'))
File "/usr/lib64/python3.9/importlib/__init__.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "", line 1030, in _gcd_import
File "", line 1007, in _find_and_load
File "", line 972, in _find_and_load_unlocked
File "", line 228, in _call_with_frames_removed
File "", line 1030, in _gcd_import
File "", line 1007, in _find_and_load
File "", line 984, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'confluent.docker_utils'
```

Start by inspecting setup.py, requirements.txt, and the contents of the generated source archive. Reproduce the setup.py sdist and pip install commands, then verify that the archive includes its requirements and package modules so installation succeeds and the cub and dub entry points can import confluent.docker_utils.

Written by the indexing model from the issue text.