soroban-rpc: Allow Budget Instruction Leeway to be Configured by Clients #3105

Job	Run time
Integration tests (ubuntu-20.04, 1.21, .CLI.)	14m 32s
Build (ubuntu-latest, x86_64-unknown-linux-gnu, amd64)	2m 15s
Integration tests (ubuntu-20.04, 1.21, ^Test(([^C])\|(C[^L])\|(CL[^I])).*$)	12m 38s
Build (ubuntu-latest, aarch64-unknown-linux-gnu, arm64)	2m 57s
Build (macos-latest, x86_64-apple-darwin, amd64)	5m 33s
Build (macos-latest, aarch64-apple-darwin, arm64)	3m 47s
Build (windows-latest, x86_64-pc-windows-gnu, amd64)	8m 36s
Unit tests (ubuntu-20.04, 1.21)	5m 19s
	55m 37s

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