Creates install info file

[mx-psi]

What does this PR do?

Creates install_info file with information about the install method used (overwrites any other existing file).

Additional information

Role versioning is managed by the tags on this repository. Ansible does not provide a straightforward way of accessing that information (I requested the feature on ansible/ansible#69600).

This PR hardcodes the role version on to a variable (role_version) which would need to be updated on each new release. I think this is the most desirable option but two alternatives I considered are described below.

Alternative 1

We could run ansible-galaxy info [role name] --offline, and parse the resulting output, which looks like (abbreviated):

Role: datadog.datadog
        description:
        dependencies: []
        galaxy_info:
                [...]
        install_date: Fri May 22 10:55:03 2020
        installed_version: x.x.x
        path: ('/root/.ansible/roles', '/usr/share/ansible/roles', '/etc/ansible/roles')

this is not valid YAML; we could grep it but I don't think it is a good idea (the format might change).

Alternative 2

The version is stored in a hidden YAML file (see here) so we could retrieve and parse it. It is an internal Ansible file which I don't think we should rely on it.

Describe your test plan

Install this version of the role using

ansible-galaxy install git+https://github.com/DataDog/ansible-datadog.git,mx-psi/ansible-install-info

Run it using the repo's instructions and check that:

1. the installation succeeded and
2. the file was created with the correct information.

[KSerrania]

LGTM 🚀