dnsdist: Make recording queries/responses in the ringbuffers optional

[rgacogne]

Short description

In some setups where grepq, top* and the dynamic blocks are not used, inserting queries and/or responses into the ring buffers is not worth it, as it involves (small) CPU and memory costs.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[Habbie]

Looks good, one unrelated question (in a comment), one related question: should this deprecate setRingBuffersLockRetries?

[rgacogne]

Looks good, one unrelated question (in a comment), one related question: should this deprecate setRingBuffersLockRetries?

Yes! On it.