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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.

galaxy_type = 'collection' if parser.metavar == 'COLLECTION_ACTION' else 'role'
        init_parser = parser.add_parser('init', parents=parents,
                                        help='Initialize new {0} with the base structure of a '
                                             '{0}.'.format(galaxy_type))
        init_parser.set_defaults(func=self.execute_init)
        init_parser.add_argument('--init-path', dest='init_path', default='./',
                                 help='The path in which the skeleton {0} will be created. The default is the '
                                      'current working directory.'.format(galaxy_type))
        init_parser.add_argument('--{0}-skeleton'.format(galaxy_type), dest='{0}_skeleton'.format(galaxy_type),
                                 default=C.GALAXY_ROLE_SKELETON,
                                 help='The path to a {0} skeleton that the new {0} should be based '
                                      'upon.'.format(galaxy_type))
        obj_name_kwargs = {}
        if galaxy_type == 'collection':
            obj_name_kwargs['type'] = validate_collection_name
        init_parser.add_argument('{0}_name'.format(galaxy_type), help='{0} name'.format(galaxy_type.capitalize()),
                                 **obj_name_kwargs)
        if galaxy_type == 'role':
            init_parser.add_argument('--type', dest='role_type', action='store', default='default',
                                     help="Initialize using an alternate role type. Valid types include: 'container', "
                                          "'apb' and 'network'.")
    def add_remove_options(self, parser, parents=None):