p2p: enable GetAddr() and GetAddresses() by network

Summary:

p2p: enable CAddrMan::GetAddr_() by network, add doxygen

https://github.com/bitcoin/bitcoin/pull/21843/commits/d35ddca91ebbcf8d8b790c3b9f8cf218fafb7a53

p2p: pull time call out of loop in CAddrMan::GetAddr_()

https://github.com/bitcoin/bitcoin/pull/21843/commits/c38981e748f438d972ba12ba998c8a8a597e01c1

p2p: allow CAddrMan::GetAddr() by network, add doxygen

https://github.com/bitcoin/bitcoin/pull/21843/commits/a49f3ddbbabfb971a537f0a6c7affb24e20ff192

p2p: allow CConnman::GetAddresses() by network, add doxygen

https://github.com/bitcoin/bitcoin/pull/21843/commits/80ba294854e5025bcada58f1403858e6ea1d4380

This is a partial backport of core#21843 [1/2]

The fuzzer file does not exist in Bitcoin ABC because of missing backports.

Review hint: this first part of the backport includes all changes of the pull request except for release notes, functional tests and most changes to src/rpc/net.cpp

Test Plan:

ninja all check-all bench-bitcoin

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11127