Add Notification Retry Backoff Configuration

[Abd-Standard]

Description

Allow retry backoff behaviour to be configured independently of the notification provider implementation.

Acceptance Criteria

Backoff parameters are configurable.

Invalid values are rejected.

Retry delays remain bounded.

Configuration is documented.

[Henrichy]

@Henrichy has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi! I'd like to work on this issue.
I've contributed to Rust, TypeScript, backend, frontend, and smart contract projects, with a focus on delivering focused, well-tested changes. I'll keep the implementation within the requested scope, preserve existing behavior unless the issue requires otherwise, include the necessary tests and documentation, and submit a PR that's straightforward to review.
Portfolio: https://portfolio-sandy-alpha-29.vercel.app • ETA: ~2–4 hours.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Henrichy to this issue.

[Henrichy]

@Abd-Standard please assign this to me. Im short of issues please. Would deliver in less than 2 hours

[olalois]

@olalois has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello Maintainer, I will like to be assigned this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @olalois to this issue.

[drips-wave]

Congratulations, @olalois! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @olalois: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

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