fix: do not dial bootstrap nodes

[achingbrain]

Updates the bootstrap module to only discover the bootstrap nodes but not dial them.

Invidiual protocols that require bootstrapping (e.g. KAD-DHT) can then react to the disovery and choose to dial the peers.

This cuts down on unecessary dials for lightweight nodes and brings the bootstrap module in line with other peer discovery mechanisms.

Change checklist

• [x] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation if necessary (this includes comments as well)
• [ ] I have added tests that prove my fix is effective or that my feature works