Use debug for log about skipping addition of cert

[sylr]

What does this PR do?

This entry can flood the logs if a cert is duplicated like wildcard certs can be.

Motivation

Backport #5641 in v1.7 tree.

More

• Added/updated tests
• Added/updated documentation

Additional Notes

[sylr]

FYI, this is what happened when we deployed the v2.0 patched version:

[ldez]

Hello,

I recommend to use the level WARN (the default level) instead of INFO in your configuration.

[sylr]

Hi

I recommend to use the level WARN (the default level) instead of INFO in your configuration.

But if I do this I would lose access logs which use the INFO level, wouldn't I ?

[ldez]

The log level is for Traefik log.

Some logs in Traefik log can be interpreted as "access log" but I recommend to not use it for that.

The access logs don't have a level.

[ldez]

As much as this change made sense in the v2 because of the management of the TLS on the routers, as much on the v1 that does not seem to me relevant.

So we will declined.

Thanks anyway.