User-aware relay address generator

[enobufs]

Resolves #420

Description

Details of this feature are described in #420.
This PR make following changes:

• Adds AllocatePacketConnForUser and AllocateConnForUser methods to RelayAddressGenerator interfaces
  • These methods deprecates AllocatePacketConn and AllocateConn respectively.
• Changes to internal packages:
  • NewAllocation
  • ManagerConfig
  • CreateAllocation
  • authenticateRequest - to pass "username" to CreateAllocation method

Reference issue

Fixes #420

[codecov]

Codecov Report

Attention: Patch coverage is 36.63366% with 64 lines in your changes missing coverage. Please review.

Project coverage is 65.64%. Comparing base (3ff9392) to head (6e85c3f).

Files with missing lines	Patch %	Lines
relay_address_generator_range.go	0.00%	26 Missing ⚠️
relay_address_generator_static.go	0.00%	14 Missing ⚠️
relay_address_generator_none.go	0.00%	8 Missing ⚠️
internal/server/util.go	45.45%	6 Missing ⚠️
internal/allocation/allocation_manager.go	82.75%	4 Missing and 1 partial ⚠️
server.go	0.00%	4 Missing ⚠️
internal/server/turn.go	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #421      +/-   ##
==========================================
- Coverage   66.63%   65.64%   -0.99%     
==========================================
  Files          43       43              
  Lines        2919     2995      +76     
==========================================
+ Hits         1945     1966      +21     
- Misses        807      861      +54     
- Partials      167      168       +1     

Flag	Coverage Δ
go	65.64% <36.63%> (-0.99%)	⬇️
wasm	26.47% <1.98%> (-0.66%)	⬇️

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[enobufs]

I hoped not to make breaking change but I have to touch the public interface, a breaking change is unavoidable. I will make the change simpler.