Request: Enable custom indexers

[mainnet-pat]

If one only wants to index certain span of blockchain and/or only transactions interesting for their usecase then some optional new params like:

• indexFrom
• indexTo
• transactionFilter

would be super helpful. First two are obvious, transactionFilter is javascript function which takes in the libauth transaction and returns true if it should be saved to db or false if it should be skipped.

This would enable token-specific indexers, or protocol specific indexers - like for TapSwap, Cauldron, etc. Data footprints would be lower and query times - shorter.