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##### SUMMARY
The "source" folder of my collection contains several files that are not directly related to the collection itself. E.g. a `.gitignore`, a `.github` folder, a `Makefile` etc.
When using `ansible-galaxy collection build <folder>`, these files are included in the generated tarball. This is especially hurtful when the source folder also contains a Python venv that I use for developing.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
ansible-galaxy

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.9.0.dev0
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/home/egolov/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /home/egolov/Devel/ansible/ansible/lib/ansible
  executable location = /home/egolov/Devel/ansible/ansible/bin/ansible
  python version = 2.7.15 (default, Oct 15 2018, 15:26:09) [GCC 8.2.1 20180801 (Red Hat 8.2.1-2)]

```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below
empty
```

##### OS / ENVIRONMENT
Fedora


##### STEPS TO REPRODUCE
Build a collection :)

##### EXPECTED RESULTS
I'd expect only collection-relevant files/folders (those that are listed in the spec/docs) to be included.


##### ADDITIONAL INFORMATION
Alternatively, a ignore file as suggested by @bcoca  in https://github.com/ansible/ansible/pull/59121/files#r304554334 could be a fix for this.

test_dir = to_text(tmp_path_factory.mktemp('test-ÅÑŚÌβŁÈ Collections'))
    collection1 = os.path.join(test_dir, 'namespace1', 'collection1')
    collection2 = os.path.join(test_dir, 'namespace2', 'collection2')
    fake_collection1 = os.path.join(test_dir, 'namespace3', 'collection3')
    fake_collection2 = os.path.join(test_dir, 'namespace4')
    os.makedirs(collection1)
    os.makedirs(collection2)
    os.makedirs(os.path.split(fake_collection1)[0])
    open(fake_collection1, 'wb+').close()
    open(fake_collection2, 'wb+').close()
    collection1_manifest = json.dumps({
        'collection_info': {
            'namespace': 'namespace1',
            'name': 'collection1',
            'version': '1.2.3',
            'authors': ['Jordan Borean'],
            'readme': 'README.md',
            'dependencies': {},
        },