Webhook event for Issue updates (e.g. Jira linking)

#### Description

Currently, Sentry webhooks support events such as `issue.created`, which allows external systems to receive notifications when new Issues are created. However, there is no webhook event that notifies when an Issue is updated.

In some workflows, external services maintain a local copy of Sentry Issues for analysis purposes. When an Issue is updated — for example, when a Jira ticket is linked — it would be valuable to receive a webhook event reflecting that change, so the external system can stay in sync.

#### Use cases

* Receive notifications when an Issue is linked to a Jira ticket.
* Update external systems with up-to-date Issue state after changes.
* Maintain accurate local storage copies of Issues that reflect external integrations.

#### Proposal

* Add a new webhook event, e.g. `issue.updated` or `issue.linked`.
* Include updated data in the payload

#### Benefit

This would allow external systems to keep local data in sync with Sentry as Issues are updated, improving integration reliability and reducing the need for inefficient polling.

We want to define a set of [lightweight metrics]() that SDKs can automatically collect for e.g. framework, language or platform, focusing only on signals that **do NOT overlap with Tracing**. Ideally these metrics should give a quick sense of app or runtime health, … while deeper investigation will still rely on traces or profiles.

Examples**:**

* Node.js runtime metrics (e.g., event loop delay, heap usage)
* Prisma-related metrics in Next.js
* Mobile CPU / memory usage to help surface potential ANRs or app hangs

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**Candidate Metrics (add more below)**

* …

*(please also add ideas, questions or examples in comments)*

The issue names the existing `issue.created` webhook event but no files, tests, or entry points. Start by locating how that event is defined and delivered, then determine the update scope and payload contract. Done means an update event is emitted with updated Issue data, including changes such as Jira linking, and external systems can use it instead of polling.

Written by the indexing model from the issue text.