This patch series implements `write_consistency_levels_warned` and `write_consistency_levels_disallowed` guardrails, allowing the configuration of which consistency levels are unwanted for writes. The motivation for these guardrails is to forbid writing with consistency levels that don't provide high durability guarantees (like CL=ANY, ONE, or LOCAL_ONE).
Neither guardrail is enabled by default, so as not to disrupt clusters that are currently using any of the CLs for writes. The warning guardrail may seem harmless, as it only adds a warning to the CQL response; however, enabling it can significantly increase network traffic (as a warning message is added to each response) and also decrease throughput due to additional allocations required to prepare the warning. Therefore, both guardrails should be enabled with care. The newly added `writes_per_consistency_level` metric, which is incremented unconditionally, can help decide whether a guardrail can be safely enabled in an existing cluster.
This commit adds additional `if` instructions on the critical path. However, based on the `perf_simple_query` benchmark for writes, the difference is marginal (~40 additional instructions, which is a relative difference smaller than 0.001).
BEFORE:
```
291443.35 tps ( 53.3 allocs/op, 16.0 logallocs/op, 14.2 tasks/op, 48067 insns/op, 18885 cycles/op, 0 errors)
throughput:
mean= 289743.07 standard-deviation=6075.60
median= 291424.69 median-absolute-deviation=1702.56
maximum=292498.27 minimum=261920.06
instructions_per_op:
mean= 48072.30 standard-deviation=21.15
median= 48074.49 median-absolute-deviation=12.07
maximum=48119.87 minimum=48019.89
cpu_cycles_per_op:
mean= 18884.09 standard-deviation=56.43
median= 18877.33 median-absolute-deviation=14.71
maximum=19155.48 minimum=18821.57
```
AFTER:
```
290108.83 tps ( 53.3 allocs/op, 16.0 logallocs/op, 14.2 tasks/op, 48121 insns/op, 18988 cycles/op, 0 errors)
throughput:
mean= 289105.08 standard-deviation=3626.58
median= 290018.90 median-absolute-deviation=1072.25
maximum=291110.44 minimum=274669.98
instructions_per_op:
mean= 48117.57 standard-deviation=18.58
median= 48114.51 median-absolute-deviation=12.08
maximum=48162.18 minimum=48087.18
cpu_cycles_per_op:
mean= 18953.43 standard-deviation=28.76
median= 18945.82 median-absolute-deviation=20.84
maximum=19023.93 minimum=18916.46
```
Fixes: SCYLLADB-259
Refs: SCYLLADB-739
No backport, it's a new feature
Closesscylladb/scylladb#28570
* github.com:scylladb/scylladb:
scylla.yaml: add write CL guardrails to scylla.yaml
scylla.yaml: reorganize guardrails config to be in one place
test: add cluster tests for write CL guardrails
test: implement test_guardrail_write_consistency_level
cql3: start using write CL guardrails
cql3/query_processor: implement metrics to track CL of writes
db: cql3/query_processor: add write_consistency_levels enum_sets
config: add write_consistency_levels_* guardrails configuration
c3f59e4fa1