Running configuration exposed via `/debug/vars` endpoint

[devanbenz]

ETA: 1.12.3
PR: feat: Adds 'config' to 'debug/vars' http endpoint

The /debug/vars HTTP endpoint now includes a "config" key containing the running server configuration. This is useful for remote diagnostics and troubleshooting without needing direct access to the configuration file.

• toml.Size values are serialized as integers (bytes)
• toml.Duration values are serialized as human-readable duration strings

InfluxDB OSS and Enterprise 1.12.3+