feat(p2p)!: Extend Head interface's Head method with ...HeadOption, introduce WithTrustedHead opt

[renaynay]

This PR introduces variadic HeadOptions and adds them as optional param to the Head method in the Head interface.

It will allow callers to the Exchange's Head method to specify if subjective initialisation is required, determining which peerset (trusted or tracked) to choose from (the default is tracked) via the WithTrustedHead option.

It also exposes a getPeers endpoint on the tracker that returns its currently tracked peers.

[codecov-commenter]

Codecov Report

Merging #53 (299731a) into main (87ab66e) will increase coverage by 0.93%.
Report is 3 commits behind head on main.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##             main      #53      +/-   ##
==========================================
+ Coverage   67.27%   68.21%   +0.93%     
==========================================
  Files          35       36       +1     
  Lines        2827     2888      +61     
==========================================
+ Hits         1902     1970      +68     
+ Misses        772      766       -6     
+ Partials      153      152       -1     

Files Changed	Coverage Δ
interface.go	0.00% <ø> (ø)
headertest/dummy_header.go	65.62% <50.00%> (ø)
p2p/peer_tracker.go	77.95% <81.57%> (+0.03%)	⬆️
p2p/exchange.go	82.78% <93.47%> (+1.79%)	⬆️
headertest/dummy_suite.go	100.00% <100.00%> (ø)
headertest/store.go	88.13% <100.00%> (+5.08%)	⬆️
local/exchange.go	47.61% <100.00%> (ø)
opts.go	100.00% <100.00%> (ø)
store/store.go	68.02% <100.00%> (ø)
sync/sync_getter.go	90.47% <100.00%> (ø)
... and 1 more

... and 2 files with indirect coverage changes

The merge-base changed after approval.

[gupadhyaya]

lgtm.

[renaynay]

Updated title + description

[Wondertan]

Last nits and GTG