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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.

info = {}
        for b_file_name, property_name in CollectionRequirement._FILE_MAPPING:
            b_file_path = os.path.join(b_path, b_file_name)
            if not os.path.exists(b_file_path):
                continue
            with open(b_file_path, 'rb') as file_obj:
                try:
                    info[property_name] = json.loads(to_text(file_obj.read(), errors='surrogate_or_strict'))
                except ValueError:
                    raise AnsibleError("Collection file at '%s' does not contain a valid json string."
                                       % to_native(b_file_path))
        if 'manifest_file' in info:
            manifest = info['manifest_file']['collection_info']
            namespace = manifest['namespace']
            name = manifest['name']
            version = manifest['version']
            dependencies = manifest['dependencies']
        else:
            display.warning("Collection at '%s' does not have a MANIFEST.json file, cannot detect version."
                            % to_text(b_path))
            parent_dir, name = os.path.split(to_text(b_path, errors='surrogate_or_strict'))
            namespace = os.path.split(parent_dir)[1]
            version = '*'
            dependencies = {}
        meta = CollectionVersionMetadata(namespace, name, version, None, None, dependencies)
        files = info.get('files_file', {}).get('files', {})
        return CollectionRequirement(namespace, name, b_path, None, [version], version, force, parent=parent,
                                     metadata=meta, files=files, skip=True)
    @staticmethod
    def from_name(collection, apis, requirement, force, parent=None):