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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.

company='your company (optional)',
                license='license (GPL-2.0-or-later, MIT, etc)',
                role_name=obj_name,
                role_type=context.CLIARGS['role_type'],
                issue_tracker_url='http://example.com/issue/tracker',
                repository_url='http://example.com/repository',
                documentation_url='http://docs.example.com',
                homepage_url='http://example.com',
                min_ansible_version=ansible_version[:3],  
            ))
            obj_path = os.path.join(init_path, obj_name)
        elif galaxy_type == 'collection':
            namespace, collection_name = obj_name.split('.', 1)
            inject_data.update(dict(
                namespace=namespace,
                collection_name=collection_name,
                version='1.0.0',
                readme='README.md',
                authors=['your name <example@domain.com>'],
                license=['GPL-2.0-or-later'],
                repository='http://example.com/repository',
                documentation='http://docs.example.com',
                homepage='http://example.com',
                issues='http://example.com/issue/tracker',
            ))
            obj_path = os.path.join(init_path, namespace, collection_name)
        b_obj_path = to_bytes(obj_path, errors='surrogate_or_strict')
        if os.path.exists(b_obj_path):
            if os.path.isfile(obj_path):
                raise AnsibleError("- the path %s already exists, but is a file - aborting" % to_native(obj_path))