Set minimum values for LS

[kwek20]

Description

Sets minimum values to pruning delay and depth for local snapshots

Fixes #1217

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

Unit tests

[jakubcech]

Just to add here, I changed the minimum value to 40,000, instead of the first proposed 30,000. It better represents 30 days of transactions, and also more suitable for back references.

[DyrellC]

@jakubcech So we don't want to have the option to store less than 30 days of transactions for LS nodes? I've had several nodes running on much less and the DB's have been very small as a result, and the nodes have had no problem operating longer term. Is this a minimum that may change in the future to accommodate the smaller devices that may not want to be storing a full 30 days?

[jakubcech]

I expect the value to change, possibly so in the not too far off future.