Postgresql-14 and Postgresql-15 support in pghoard 2.2.1

# What is currently missing?

As of now pghoard 2.2.1 support for pgsql-14 is missing.

# How could this be improved?

pghoard/config.py contains the supported versions list . PGSQL version 14 could be added to get pghoard compatible with db.
SUPPORTED_VERSIONS = ["14", "13", "12", "11", "10", "9.6", "9.5", "9.4", "9.3"]

Also the document does not specify if postgresql 13 and 14 are supported/tested.It mentions until version 12.
But in the config.py , we can see supported versions until 13.
This creates a confusion if the software will work with latest databases.

# Is this a feature you would work on yourself?

If you could commit this change that would be great.