New `time_format` query parameter for HTTP API

[devanbenz]

ETA: 1.12.3
PR: feat: Adds time_format param for httpd

A new time_format query parameter has been added to the /query HTTP API endpoint.

• Accepted values: rfc3339, epoch (default: epoch)
• When set to rfc3339, timestamps in query results are returned as RFC3339Nano formatted strings
• When set to epoch, the existing epoch precision parameter continues to work as before
• Invalid values return a 400 Bad Request

InfluxDB OSS and Enterprise 1.12.3+