feat(repos): Activate repo webhook and syncing task for GHE

[wedamija]

This enables the same github syncing for GHE

[sentry]

Bug: The GitHubEnterpriseWebhookEndpoint uses @cell_silo_endpoint, but middleware routes installation_repositories events to the CONTROL silo, causing a routing conflict and request failure.
_{Severity: HIGH}

Suggested Fix

Change the decorator on GitHubEnterpriseWebhookEndpoint from @cell_silo_endpoint to @all_silo_endpoint. This will allow the endpoint to execute in both CELL and CONTROL silos, resolving the conflict with the middleware's routing logic for control-only events.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: src/sentry/integrations/github_enterprise/webhook.py#L355-L361

Potential issue: There is a silo routing conflict for the GitHub Enterprise
`installation_repositories` webhook event. The middleware correctly identifies this
event as control-silo-only and routes the request to the CONTROL silo. However, the
`GitHubEnterpriseWebhookEndpoint` is decorated with `@cell_silo_endpoint`, which
enforces that it can only run in the CELL silo. When the request is dispatched in
CONTROL silo mode, the decorator will reject it, resulting in a 404 error or an
`AvailabilityError`. This will cause webhook deliveries for repository updates to fail,
preventing repository data from being synchronized.

_{Did we get this right? 👍 / 👎 to inform future reviews.}