docs(config): add configuration guides

[317787106]

What does this PR do?

1. Rewrites reference.conf comments — every parameter now has an inline comment describing its purpose, valid range, and unit. The file is the authoritative default-value reference for all node operators and contributors.

2. Slims down config.conf — removes the large duplicated comment blocks that belonged in reference.conf, leaving only the parameters whose shipped defaults intentionally differ from reference.conf and the minimal comments users need to act on.

3. Fixes default values for three under-specified parameters:

   • node.rpc.maxConcurrentCallsPerConnection: Integer.MAX_VALUE → 0 (0 = no limit）
   • node.rpc.maxConnectionIdleInMillis / maxConnectionAgeInMillis: changed to 0 (0 = no limit）
   • node.dns.maxMergeSize: 1 → 5; changeThreshold: 0.8 → 0.1 (align with actual recommended values)

4. Adds two documentation files under docs/:

   • configuration.md — user-facing guide: explains the reference.conf / config.conf two-layer system, how to start a node with a config file, and the most common configuration sections with examples.
   • configuration-conventions.md — developer-facing guide: covers ConfigBeanFactory auto-binding rules, the camelCase naming requirement, nesting depth limits, the four-step checklist for adding a new parameter, special type handling (List<String>, human-readable sizes), and backward-compatibility patterns.

Why are these changes required?

config.conf previously duplicated most of reference.conf's comment content, making it hard to maintain and causing users to question which file to trust. Meanwhile reference.conf lacked inline documentation for many parameters. There was also no written guide explaining the two-layer config system or the conventions developers must follow when extending it, leading to inconsistencies (non-camelCase keys, missing reference.conf entries, etc.).

This PR has been tested by

• Unit Tests
• Manual Testing