Continuous query diagnostics exposed via `/debug/vars` endpoint

[devanbenz]

ETA: 1.12.3
PR: feat: Adds 'cq' diagnostics to /debug/vars

The /debug/vars HTTP endpoint now includes continuous query (CQ) diagnostic information under a "cq" key. This aids in monitoring and troubleshooting continuous query execution.

InfluxDB OSS and Enterprise 1.12.3+