Fix RPC Webhook queue dropping

[WietseWind]

Problem:

When using subscribe at admin RPC port to send webhooks for the transaction stream to a backend, on large(r) ledgers the endpoint was consistently receiving fewer HTTP POSTs with TX information than the amount of transactions in a ledger.

This resulted in some XamanWallet users, on larger ledgers, not always receiving their transaction push notifications.

Details

Admin command RPC Post to URL had a 32 queue length (hardcoded) resulting in dropping TX notifications.

1. As this is an admin-command only, I stripped out the entire queue length check. If admin, you should know what you are doing. If your endpoint can't efficiently handle the TPS, your problem.

2. Also: shorter TTL for outgoing RPC HTTP calls: was 10 minutes PER REQUEST, now is 30 seconds (still too long, but 10 minutes is a guaranteed shit show if the calls keep on hanging and stack up, especially since the 32 queue length for HTTP calls is now removed).

While dropping the queue length limit on sent WebHooks could be considered dangerous, it's guarded by admin-RPC port anyway:

rippled/src/xrpld/rpc/handlers/Subscribe.cpp

Line 51 in 63209c2

if (context.role != Role::ADMIN)

Finally:

3. Change timeout const to be less ambiguous.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.1%. Comparing base (33e1c42) to head (9bc8719).

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #5163   +/-   ##
=======================================
  Coverage     78.1%   78.1%           
=======================================
  Files          790     790           
  Lines        67556   67553    -3     
  Branches      8158    8154    -4     
=======================================
+ Hits         52785   52792    +7     
+ Misses       14771   14761   -10     

Files with missing lines	Coverage Δ
src/xrpld/net/detail/RPCCall.cpp	94.3% <100.0%> (ø)
src/xrpld/net/detail/RPCSub.cpp	45.5% <ø> (+1.7%)	⬆️

... and 4 files with indirect coverage changes

[godexsoft]

Agree with @mvadari that the code comments should be removed. Also added a question.

[WietseWind]

@mvadari comments removed.