Add support for CheckMK password store

[computergeek125]

When the password store is enabled for this agent, the check fails and generates this error:

[special_unifi_controller]: agent_unifi_controller: error: unrecognized arguments: --pwstore=4@0@[redacted]

Looks like it might be straightforward to add a decryptor - https://github.com/Checkmk/checkmk/blob/master/cmk/utils/password_store.py

Might be able to PR this one myself if I get a few minutes to spare, just adding this issue for those coming in from Google.

For those who found this issue, the workaround is to set an explicit password in the agent configuration rather than using a password vault entry