repo: add an Enhancement issue-template

[ghost]

Summary

The Enhancement label is there, and clearly the dev-processes here distinguish between New-Feature and Enhancement (see additionally the PR processing).

So there is no reason to not provide an issue-template, thus users can pick it right from the beginning:

https://github.com/algorand/go-algorand/issues/new/choose

Test Plan

a little bit on own repo, but is trivial

(please feel free to close this PR and create the template with your requirements from the github UI - should be here:

• https://github.com/algorand/go-algorand/issues/templates/edit)

[codecov]

Codecov Report

Merging #5091 (2cfc784) into master (8e5df38) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5091   +/-   ##
=======================================
  Coverage   53.53%   53.53%           
=======================================
  Files         430      430           
  Lines       54086    54086           
=======================================
+ Hits        28954    28955    +1     
+ Misses      22880    22879    -1     
  Partials     2252     2252           

Impacted Files	Coverage Δ
ledger/voters.go	68.65% <0.00%> (-4.48%)	⬇️
ledger/blockqueue.go	82.25% <0.00%> (-2.69%)	⬇️
network/wsPeer.go	65.50% <0.00%> (-1.87%)	⬇️
cmd/tealdbg/debugger.go	71.65% <0.00%> (-0.79%)	⬇️
network/wsNetwork.go	65.04% <0.00%> (-0.19%)	⬇️
ledger/acctonline.go	78.64% <0.00%> (ø)
ledger/acctupdates.go	69.24% <0.00%> (+0.48%)	⬆️
ledger/catchpointtracker.go	57.92% <0.00%> (+0.78%)	⬆️
catchup/peerSelector.go	100.00% <0.00%> (+1.04%)	⬆️
catchup/service.go	69.80% <0.00%> (+1.20%)	⬆️
... and 1 more

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[ghost]

@barnjamin

[ghost]

@barnjamin , ty!

@algorandskiy , looks like this one needs 2 approvals...