feat(ledger): sig->agave ledger migration tool

[Sobeston]

This is for when you have a ledger from Sig, but want to cross-validate with Agave (or vice versa).

This tool will take in your Sig ledger directory, and a (new) agave ledger directory, and port the data over.

Usage:

1. Make a new directory for your agave ledger
2. Check out this branch, and build sig (recommend doing a release build)
3. run sig agave-migration-tool -i sig-ledger-dir -o agave-ledger-dir
4. copy the AccountsDB snapshots from sig to agave-ledger-dir/remote
5. run agave with e.g. (the agave ledger tool will not work until the validator command is used first)

$bin/agave-validator --identity $identity --ledger $ledger --entrypoint entrypoint.testnet.solana.com:8001 --entrypoint entrypoint2.testnet.solana.com:8001 --entrypoint entrypoint3.testnet.solana.com:8001 --rpc-port 8899 --no-voting --no-snapshots   --no-snapshot-fetch --use-snapshot-archives-at-startup always --limit-ledger-size 50000000000000 

[InKryption]

Just some basic naming nits, otherwise lgtm.

[codecov]

Codecov Report

❌ Patch coverage is 98.38710% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/ledger/database/agave_migration.zig	97.56%	1 Missing ⚠️

Files with missing lines	Coverage Δ
src/ledger/Ledger.zig	88.23% <100.00%> (ø)
src/ledger/Reader.zig	89.50% <100.00%> (ø)
src/ledger/database/hashmap.zig	86.15% <ø> (ø)
src/ledger/database/interface.zig	99.71% <100.00%> (ø)
src/ledger/database/rocksdb.zig	99.34% <ø> (ø)
src/ledger/tests.zig	90.05% <100.00%> (ø)
src/ledger/database/agave_migration.zig	97.56% <97.56%> (ø)

... and 4 files with indirect coverage changes

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[yewman]

Suggested change

	.short = "Convert a between Sig and Agave ledger formats",
	.short = "Convert between Sig and Agave ledger formats",

[yewman]

Can we add the full instruction list here as specified in the PR description? I would like to avoid any users getting confused if attempting to use the ledger tool directly before running Agave validator which fixes up the ledger after conversion