thread safety annotation for m_tx_relay_mutex and m_cached_tip_mutex

Summary:
This is a partial backport of core#24931
https://github.com/bitcoin/bitcoin/pull/24931/commits/f24bd45b37e1b2d19e5a053dbfefa30306c1d41a
https://github.com/bitcoin/bitcoin/pull/24931/commits/be6aa72f9f8d50b6b5b19b319a74abe7ab4099ff
Depends on D14890

Test Plan:
After D14894:

cmake .. -GNinja -DCMAKE_BUILD_TYPE=Debug -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
ninja all check-all`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14891