Node with only autopeers takes no measures when left behind

[Alex6323]

Bug description

A Bee node that is connected to the network only through autopeers can get left behind, which means that it missed a particular milestone, and therefore cannot make any progress.

Rust version

rustc 1.58.1 (db9d1b20b 2022-01-20)

Bee version

bee-node 0.3.0-rc3 commit: 662feb8712a49681926ab6e8cde29ab30b14d1c7 branch: alex6323/pruning-mitigation-investigation

Hardware specification

Linux bee-3 4.19.0-17-amd64 #1 SMP Debian 4.19.194-3 (2021-07-18) x86_64 GNU/Linux

Steps To reproduce the bug

Explain how the maintainer can reproduce the bug.

1. Run the node
2. wait a few hours

Expected behaviour

The node realizes that it doesn't make any progress (next milestone is not arriving in a "long" time), drops all of its current autopeers, and searches for new ones until it can make progress again.

Actual behaviour

The node is left behind, and keeps its current autopeers that cannot help with staying in sync with the network.