Document the SorobanRpc -> rpc migration and min stellar-sdk version

[Jaydbrown]

Several stale PRs import SorobanRpc from @stellar/stellar-sdk. State the supported range and the internal alias, and add an ESLint no-restricted-imports rule for the old name.

[samueldoo]

Hello Maintainer, I’d love to take ownership of this issue and submit a high-quality pull request once completed.

[ZacLou]

I'd like to work on this issue. I have relevant experience with this tech stack and can deliver a clean, well-tested PR. I can submit within 1-2 days.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@ZacLou's PR #656 was approved and merged by @Jaydbrown.

🏆 @ZacLou: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (818 total points). Track your full progress on GrantFox.

👏 Great work, @ZacLou! Keep contributing to conduit-protocol.