Update getEvents docs

[psheth9]

Update getEvents doc based on https://github.com/stellar/soroban-rpc/pull/230

• Add EndLedger in GetEventsRequest. This provides finer control and clarity on the range of ledgers being queried.
• This change enhances the scalability and can now support a larger retention window (~7 days) for events.
• Ledger Scanning Limitation: The getEvents RPC will now scan a maximum of 10,000 ledgers per request. This limits the resource usage and ensures more predictable performance, especially for queries spanning large ledger ranges.

[mollykarcher]

This change enhances the scalability and can now support a larger retention window (~7 days) for events.

Maybe we defer this change until p22, since @aditya1702 is planning on testing up to 7 days at a later time

[aditya1702]

I think this will need to wait since we are not releasing all the breaking changes in P22 now (due to the SDK backward compatibility issues).

cc @Shaptic @mollykarcher