Config max_block_time does not match chain's block time in integration tests

[hu55a1n1]

Summary

Currently, max_block_time defaults to Duration::default(), but since #1917 uses this parameter to calculate block delay, it is important that it matches the max block time of the chain we're testing against.
https://github.com/informalsystems/ibc-rs/blob/master/tools/test-framework/src/types/single/node.rs#L143-L144

Acceptance Criteria

• The default value matches gaiad's default (?)
• The value matches the block time for the chain being tested against.
• Addition of a failing integration test where max_block_time doesn't match the chain's block time.
  - moved to https://github.com/informalsystems/ibc-rs/pull/2032
• Change default max_block_time to 30s

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate milestone (priority) applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned