Remove dependency on Tendermint Core

[thanethomson]

This PR entirely removes tm-load-test's dependency on the Tendermint Core Go package. This is temporary while Informal Systems readies its fork of Tendermint Core.

As such, some rudimentary functionality and types had to be replicated in the loadtest package. This will most likely be removed in future.

Instead of manually constructing a Tendermint node in an integration test, this now sets up a 4-node localnet and executes a standalone and coordinated load test against this 4-node network, while still preserving the coverage.

[codecov-commenter]

Codecov Report

Merging #168 (b4d90b9) into main (a9c21a5) will increase coverage by 8.13%.
The diff coverage is 57.89%.

@@            Coverage Diff             @@
##             main     #168      +/-   ##
==========================================
+ Coverage   52.70%   60.84%   +8.13%     
==========================================
  Files          16       18       +2     
  Lines        1958     2056      +98     
==========================================
+ Hits         1032     1251     +219     
+ Misses        825      678     -147     
- Partials      101      127      +26     

Impacted Files	Coverage Δ
pkg/loadtest/rpc.go	46.15% <46.15%> (ø)
pkg/loadtest/rand.go	50.00% <50.00%> (ø)
pkg/loadtest/client_kvstore.go	66.66% <100.00%> (ø)
pkg/loadtest/coordinator.go	72.47% <100.00%> (+2.52%)	⬆️
pkg/loadtest/loadtest.go	59.57% <100.00%> (+23.40%)	⬆️
pkg/loadtest/tm_network_info.go	77.22% <100.00%> (+77.22%)	⬆️
pkg/loadtest/transactor.go	61.75% <100.00%> (ø)
pkg/loadtest/worker.go	58.82% <0.00%> (+4.97%)	⬆️
... and 1 more