Allow to override the default templates

[ariandres]

This is an implementation proposition for https://github.com/geerlingguy/ansible-role-ntp

It does not change the default role's behaviour and allows user to override the default provided template with their own.

[stale[bot]]

This pull request has been marked 'stale' due to lack of recent activity. If there is no further activity, the PR will be closed in another 30 days. Thank you for your contribution!

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[stale[bot]]

This pull request has been closed due to inactivity. If you feel this is in error, please reopen the pull request or file a new PR with the relevant details.