[epic] Remove horizon dependency for sendTransaction and getTransactionStatus endpoints

[tamirms]

soroban-rpc currently uses horizon for submitting transactions and obtaining transaction results. Given that soroban-rpc is now running captive core, we should be able to come up with a new architecture where transaction submission in soroban-rpc does not depend on horizon.

This issue will be complete when:

• the design for soroban txsub without horizon is proposed and approved: soroban-rpc: design transaction submission without horizon #444
• the implementation of the design is merged: soroban-rpc: implement transaction submission #445
• remove horizon from soroban rpc requirements:
  • quickstart: remove horizon from soroban-dev image quickstart#430
  • system-test: remove references to horizon system-test#32
  • helm: sdf helm chart config
• update soroban-cli to reflect new API: soroban-cli: update to reflect the new transaction APIs #446
• update soroban js client to reflect new API: Update to reflect the new transaction APIs js-soroban-client#51
• update docs to reflect new API: Update to reflect the changes to the transaction API stellar-deprecated/soroban-docs#333

We should make sure the design and implementation also addresses these related issues:

• soroban-rpc: Improve sendTransaction/getTransactionStatus error reporting go#4642
• soroban-rpc: Add eta field for transactions for more efficient polling #372
• soroban-rpc: Deprecate getTransactionStatus.results field #339
• soroban-rpc proposal: only serve ingested transactions #413

[tomerweller]

see #413