rpc/jsonrpc/server: merge WriteRPCResponseHTTP and WriteRPCResponseAr

[melekes]

...rrayHTTP

Closes #5135

Also, wrote a test for WriteRPCResponseHTTPError and used it with correct status codes according to https://www.jsonrpc.org/historical/json-rpc-over-http.html#response-codes

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[codecov]

Codecov Report

Merging #5141 into master will increase coverage by 0.02%.
The diff coverage is 55.55%.

@@            Coverage Diff             @@
##           master    #5141      +/-   ##
==========================================
+ Coverage   62.61%   62.63%   +0.02%     
==========================================
  Files         256      256              
  Lines       27161    27172      +11     
==========================================
+ Hits        17007    17020      +13     
- Misses       8658     8664       +6     
+ Partials     1496     1488       -8     

Impacted Files	Coverage Δ
rpc/jsonrpc/server/http_uri_handler.go	39.82% <0.00%> (-1.09%)	⬇️
rpc/jsonrpc/server/http_json_handler.go	63.38% <60.00%> (-0.20%)	⬇️
rpc/jsonrpc/server/http_server.go	59.82% <100.00%> (+4.73%)	⬆️
consensus/reactor.go	75.81% <0.00%> (-2.91%)	⬇️
consensus/state.go	72.05% <0.00%> (-0.83%)	⬇️
statesync/messages.go	86.20% <0.00%> (-0.75%)	⬇️
blockchain/v0/pool.go	79.29% <0.00%> (-0.32%)	⬇️
blockchain/v2/reactor.go	35.92% <0.00%> (+1.48%)	⬆️
types/tx.go	93.10% <0.00%> (+3.44%)	⬆️
... and 4 more

[tac0turtle]

ACK. pending linting fixes