docs(autofix): correct Slack feature access label from beta to Early Adopter (#17350)

## What

The "Autofix in Slack" section of the Autofix docs incorrectly described
the feature as being in "beta," which implied open/public beta access.
In reality, this feature is gated behind the
`organizations:seer-slack-workflows` Flagpole flag, which lives in
`ea-features.json` — meaning it's an **Early Adopter (EA)** feature, not
open beta.

## Changes

- Removed `[Beta]` suffix from the section heading
- Replaced the generic beta alert with an accurate Early Adopter alert
that links to the org settings page where EA can be enabled

## Why

The previous copy would lead customers to believe the feature was
broadly available or rolling out publicly, when it actually requires
opting into the Early Adopter program.

Action taken on behalf of Rahul Chhabria.

Co-authored-by: junior <junior@sentry.io>

Author: sentry-junior[bot]

docs/product/ai-in-sentry/seer/autofix/index.mdx

@@ -83,10 +83,10 @@ snippets and examples, and does not affect workflows involving your own coding a
 
 ![Screenshot of Seer showing code it generated =800x](../img/coding-step.png)
 
-## Autofix in Slack [Beta]
+## Autofix in Slack
 
 <Alert>
-This feature is currently in <strong>beta</strong>. Beta features are still a work in progress and may have bugs. We recognize the irony.
+This feature is available to organizations enrolled in the <strong>Early Adopter</strong> program. To access it, enable Early Adopter features in your [organization settings](https://sentry.io/orgredirect/organizations/:orgslug/settings/#earlyAdopter).
 </Alert>
 
 If you have the [Slack integration](/organization/integrations/notification-incidents/slack/) enabled, you can trigger Autofix from a Slack message.