Improve configuration max_block_time validation

[ljoss17]

Summary

For the max_block_time configuration Hermes will query the value on chain and verify if the configured value matches the queried value.

In Hermes v1.10.1, if the max_block_time is not configured, it will default to 30s and the value will be updated with the queried max_expected_time_per_block if it differs from 30s.

From this discussion, #4144 (comment), the desired behaviour would be the following:

• If max_block_time is configured:
  • Query max_expected_time_per_block and output a warning if the queried value differs from the configured one, but keep the configured value
  • If the query fails, keep the configured value
• If max_block_time is not configured:
  • Query max_expected_time_per_block and use that value for max_block_time
  • If the query fails, use the default value, 30s, for max_block_time

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[ancazamfir]

It's worth to review the handling of other configuration options as part of this issue, i believe there might be more cases like this as i see some cmd.override_config() calls for example. At some point a small doc that describes the general approach would be also good.

All said, i think this should be low priority.