<!--- Verify first that your issue is not already reported on GitHub -->
<!--- Also test if the latest release and devel branch are affected too -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### 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.

actual = collection._get_galaxy_yml(galaxy_yml)
    assert actual['license_ids'] == ['MIT']
def test_build_ignore_files_and_folders(collection_input, monkeypatch):
    input_dir = collection_input[0]
    mock_display = MagicMock()
    monkeypatch.setattr(Display, 'vvv', mock_display)
    git_folder = os.path.join(input_dir, '.git')
    retry_file = os.path.join(input_dir, 'ansible.retry')
    os.makedirs(git_folder)
    with open(retry_file, 'w+') as ignore_file:
        ignore_file.write('random')
        ignore_file.flush()
    actual = collection._build_files_manifest(to_bytes(input_dir), 'namespace', 'collection')
    assert actual['format'] == 1
    for manifest_entry in actual['files']:
        assert manifest_entry['name'] not in ['.git', 'ansible.retry', 'galaxy.yml']
    expected_msgs = [
        "Skipping '%s' for collection build" % to_text(retry_file),
        "Skipping '%s' for collection build" % to_text(git_folder),
    ]
    assert mock_display.call_count == 2
    assert mock_display.mock_calls[0][1][0] in expected_msgs
    assert mock_display.mock_calls[1][1][0] in expected_msgs
def test_build_ignore_older_release_in_root(collection_input, monkeypatch):