Establish p2p channel via broker

[anjmao]

1. Key and config exchange for p2p via broker.
2. Migrated p2p messages to protobuf.
3. P2P channel rewritten with raw kcp library UDP session.

Consumer will not use p2p channel yet, so old flow should work as is, but I want to review and merge it as we are getting merge conflicts.

TODO for next PRs:

1. Pass service type to channel creation so it can work for multiple services (Provider side).
2. Enable p2p channel on consumer side.
3. Pass second punched UDP conn to services (Consumer side).
4. Add internal message send retry.

[codecov-io]

Codecov Report

Merging #1922 into master will increase coverage by 0.56%.
The diff coverage is 51.44%.

@@            Coverage Diff             @@
##           master    #1922      +/-   ##
==========================================
+ Coverage   47.48%   48.05%   +0.56%     
==========================================
  Files         286      287       +1     
  Lines       12108    12595     +487     
==========================================
+ Hits         5750     6053     +303     
- Misses       5878     5985     +107     
- Partials      480      557      +77     

Impacted Files	Coverage Δ
core/connection/stats.go	70.00% <ø> (ø)
core/service/subscription.go	0.00% <0.00%> (ø)
nat/traversal/noop.go	0.00% <0.00%> (ø)
services/wireguard/connection/connection.go	58.95% <0.00%> (-2.12%)	⬇️
session/dto.go	42.85% <0.00%> (-17.15%)	⬇️
session/pingpong/exchange_messaging.go	0.00% <0.00%> (ø)
session/pingpong/factory.go	0.00% <0.00%> (ø)
session/pingpong/invoice_messaging.go	0.00% <0.00%> (ø)
tequilapi/client/dto.go	0.00% <ø> (ø)
tequilapi/endpoints/connection_location.go	85.36% <ø> (ø)
... and 29 more

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