[Chronik] Add /validate-tx endpoint

Summary:
Validates a single tx according to SLP/ALP rules without broadcasting it and returns the resulting Tx.

This is helpful for services that take raw txs and want to do some checks on them before broadcasting.

Depends on D15370.

Test Plan: ninja check-functional

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D15371