Add details about how to save state across live reloads

[mcruzdev]

This PR adds details on writing-extension.adoc, about how to persist context across live reloads.

Fixes #44288

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[quarkus-bot]

Status for workflow Quarkus CI

This is the status report for running Quarkus CI on commit cbceabd.

Failing Jobs

Status	Name	Step	Failures	Logs	Raw logs	Build scan
✖	Initial JDK 17 Build	Build	Failures	Logs	Raw logs	🔍

You can consult the Develocity build scans.

Failures

⚙️ Initial JDK 17 Build #

- Failing: extensions/smallrye-jwt/deployment 
! Skipped: docs integration-tests/management-interface-auth integration-tests/smallrye-jwt-oidc-webapp and 2 more

📦 extensions/smallrye-jwt/deployment

✖ Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.13.0:compile (default-compile) on project quarkus-smallrye-jwt-deployment: Compilation failure

[github-actions]

🙈 The PR is closed and the preview is expired.

[sberyozkin]

Thanks @mcruzdev, added minor suggestions

[sberyozkin]

@mcruzdev Looks like you opened this PR on top of the existing branch for #44272, please open it in a new branch opened on top of main

[mcruzdev]

@mcruzdev Looks like you opened this PR on top of the existing branch for #44272, please open it in a new branch opened on top of main

Yes, I made a mistake. I fixed it :)

[quarkus-bot]

Status for workflow Quarkus Documentation CI

This is the status report for running Quarkus Documentation CI on commit 8197835.

✅ The latest workflow run for the pull request has completed successfully.

It should be safe to merge provided you have a look at the other checks in the summary.

[geoand]

Thanks!