Updates mempool defaults in config.go

[cordt-sei]

• Update defaults for mempool [add TTL >0]
• Simplify / clarify related comments.

Describe your changes and provide context

These changes are intended to alleviate the issues with mempool filling to max which potentially affects the entire network as they persistently gossip these invalid txs to the rest of the network who may not have the blacklsit enabled ontop of having an infinite TTL

Testing performed to validate your change

I have been running these configs for months on my node with relatively few issues.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.20%. Comparing base (4e81a6e) to head (76b6456).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #279      +/-   ##
==========================================
+ Coverage   58.05%   58.20%   +0.15%     
==========================================
  Files         249      249              
  Lines       34662    34662              
==========================================
+ Hits        20123    20176      +53     
+ Misses      12945    12885      -60     
- Partials     1594     1601       +7     

Files with missing lines	Coverage Δ
config/config.go	63.05% <100.00%> (ø)

... and 17 files with indirect coverage changes

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