Don't exit dnsdist on an exception in maintenance

[pieterlexis]

Short description

dnsdist would exit if an exception was thrown in the maintenance function.

This change logs every minute if the maintenance function throws an exception.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled and tested this code

[phonedph1]

Nice! Fixes the biggest complaint in #4312

[rgacogne]

This should probably be decremented by interval instead of one, in case we decide to make the interval duration configurable.

[pieterlexis]

we might amend the assignment of secondsToWaitLog to that configuration setting. as the decrement then still happens every second?

[rgacogne]

If interval is not guaranteed to be equal to 1 anymore, the decrement won't happen every second except if we alter the code to do so. This would probably be needed to keep the cache cleaning delay consistent anyhow.

[rgacogne]

Perhaps we could catch std::runtime_error, or even std::exception instead of LuaContext::ExecutionErrorException? Because otherwise we don't catch LuaContext::SyntaxErrorException nor LuaContext::WrongTypeException for example, although I'm not sure they can be raised in that context.