Retry up to 3 times on password authentication failure

[rehanzo]

Resolves https://github.com/Duncaen/OpenDoas/issues/82

https://github.com/Duncaen/OpenDoas/pull/102 was closed a few days ago, so I decided to take my shot. Took a look at the comments you left, and based my changes on that.

For the pam loop, I took a look and retrying authentication with a loop seems like an expected thing to do. From https://www.ibm.com/docs/en/aix/7.2?topic=p-pam-authenticate-subroutine:

On failure, it is the responsibility of the calling application to maintain a count of authentication attempts and to reinvoke the subroutine if the count has not exceeded a defined limit.