[cmake] Handle FindBoost.cmake deprecation

Summary:
See https://cmake.org/cmake/help/latest/policy/CMP0167.html.

Starting with cmake 3.30 the FindBoost.cmake module is no longer provided and we should use the BoostConfig.cmake provided by Boost. But this file is only available since Boost 1.70.
Work around this by trying the config first then fall back to the module. There are cases where this will fail, e.g. Boost 1.64 (our current minimum) with cmake 3.30 but it's unlikely to have a system with both such a recent cmake and such an old Boost. Also there is no solution to this problem.

Test Plan:

ninja check

Run the GUIX builds

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17431