Walk seed probably conflicting default config

[CharlieC3]

Originally found by @kantai, just reporting it here.

The default value for walk_seed_probability is 10%, however this states the walk seed probably should be closer to 100%.

Furthermore it appears this constant for seed walk probably is unused.

The default value for the walk seed probably should likely be increased to align with the recommendation and expectations.

[Jiloc]

Not related to walk_seed_probability but also BurnchainConfig::poll_time_secs is set to a test value by default, instead of the suggested one for production.

https://github.com/stacks-network/stacks-core/blob/9dd349d81ce828f0b16e007bdf87331bf7fc602b/stackslib/src/config/mod.rs#L1350-L1356

https://github.com/stacks-network/stacks-core/blob/9dd349d81ce828f0b16e007bdf87331bf7fc602b/stackslib/src/config/mod.rs#L1595

In case we want to address both