Update account_subtree_height to 6

[georgeee]

Explain your changes:

• Update account_subtree_height parameter to speed up sync ledger algorithm
• Previous value of 3 was causing the algorithm to make far too many tiny RPC requests

Explain how you tested your changes:

• Tested on a small cluster: deployed with small (200 accounts) genesis ledger, grew the ledger to ~200k accounts, repeatedly deleted a pod and allowed it to bootstrap
• Tested various values for the constant (see gist), chose the best

Checklist:

• Dependency versions are unchanged
  • Notify Velocity team if dependencies must change in CI
• Modified the current draft of release notes with details on what is completed or incomplete within this project
• Document code purpose, how to use it
  • Mention expected invariants, implicit constraints
• Tests were added for the new behavior
  • Document test purpose, significance of failures
  • Test names should reflect their purpose
• All tests pass (CI will check this if you didn't)
• Serialized types are in stable-versioned modules
• Does this close issues? List them

• Closes slow bootstrap- update sync ledger message size #14202

[deepthiskumar]

!ci-build-me

[deepthiskumar]

!ci-nightly-me

[georgeee]

!ci-build-me

[deepthiskumar]

!ci-nightly-me

[deepthiskumar]

niightly run https://buildkite.com/o-1-labs-2/mina-end-to-end-nightlies/builds/589#_

[deepthiskumar]

!approved-for-mainnet