v1.18: rpc-sts: add config options for stake-weighted qos (backport of #197)

[mergify]

Problem

no simple way to configure an rpc node to send transactions to staked peer(s), as per stake-weighted qos

Summary of Changes

• adds --rpc-send-transaction-tpu-peer HOST:PORT to specify a specific tpu peer to send transctions to, instead of the current leader. this argument may be passed multiple times.
• adds --rpc-send-transaction-also-leader to continue sending to the current leader even though tpu peers have been specified with --rpc-send-transaction-tpu-peer HOST:PORT

---

This is an automatic backport of pull request #197 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of f41fb84 has failed:

On branch mergify/bp/v1.18/pr-197
Your branch is up to date with 'origin/v1.18'.

You are currently cherry-picking commit f41fb84e15.
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Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   send-transaction-service/src/send_transaction_service.rs
	both modified:   validator/src/cli.rs
	both modified:   validator/src/main.rs

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 62.50000% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 81.6%. Comparing base (5562d8d) to head (f400fa7).
Report is 2 commits behind head on v1.18.

Additional details and impacted files

@@            Coverage Diff            @@
##            v1.18     #341     +/-   ##
=========================================
- Coverage    81.6%    81.6%   -0.1%     
=========================================
  Files         827      827             
  Lines      224535   224549     +14     
=========================================
+ Hits       183310   183311      +1     
- Misses      41225    41238     +13