add configurable log format and level

[levish0]

Related to #815

Adds configurable logging output via general.log_format and general.log_level.

• add log_format with text and json modes
• add log_level using RUST_LOG compatible filter syntax
• initialize logging from config during startup
• update example.pgdog.toml and generated JSON schema

[codecov]

Codecov Report

❌ Patch coverage is 52.33645% with 51 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog/src/main.rs	30.30%	23 Missing ⚠️
pgdog/src/lib.rs	51.11%	22 Missing ⚠️
pgdog-config/src/general.rs	79.31%	6 Missing ⚠️

📢 Thoughts on this report? Let us know!

[levkk]

Nice. Reading the config twice is probably necessary here, since we also want to log config loading errors. Catch-22!

Thanks for the PR.