[pfsense_openvpn_client] Add support for additional values in digest field

[samuel-emrys]

Is your feature request related to a problem? Please describe.
The only values that can currently be passed to the digest field are SHA1 and SHA256, as per plugins/module_utils/openvpn_client.py:41:

    digest=dict(default='SHA256', required=False, choices=['SHA256', 'SHA1']),

This populates the digest xml field:

<digest>SHA256</digest>

However, pfSense also supports substantially more than these two values, including SHA224, SHA512, SHA384, MD5, among others.

Describe the solution you'd like
Entries for each of the different options in the options list

Describe alternatives you've considered
N/A

Additional context
N/A