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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.

data = self._display_role_info(role_info)
            
            
            if not data:
                data = u"\n- the role %s was not found" % role
        self.pager(data)
    def execute_install(self):
        """
        Install one or more roles(``ansible-galaxy role install``), or one or more collections(``ansible-galaxy collection install``).
        You can pass in a list (roles or collections) or use the file
        option listed below (these are mutually exclusive). If you pass in a list, it
        can be a name (which will be downloaded via the galaxy API and github), or it can be a local tar archive file.
        """
        if context.CLIARGS['type'] == 'collection':
            collections = context.CLIARGS['args']
            force = context.CLIARGS['force']
            output_path = context.CLIARGS['collections_path']
            ignore_certs = context.CLIARGS['ignore_certs']
            ignore_errors = context.CLIARGS['ignore_errors']
            requirements_file = context.CLIARGS['requirements']
            no_deps = context.CLIARGS['no_deps']
            force_deps = context.CLIARGS['force_with_deps']
            if collections and requirements_file:
                raise AnsibleError("The positional collection_name arg and --requirements-file are mutually exclusive.")
            elif not collections and not requirements_file:
                raise AnsibleError("You must specify a collection name or a requirements file.")
            if requirements_file:
                requirements_file = GalaxyCLI._resolve_path(requirements_file)
                requirements = self._parse_requirements_file(requirements_file, allow_old_format=False)['collections']
            else: