Bitbucket Server code intelligence tooltips unavailable in PR View

Created by: airamare01

• Sourcegraph version: 3.26.3+
• Platform information: Bitbucket Sever 7+

Steps to reproduce:

1. Install Sourcegraph web browser extension or plugin in Bitbucket server
2. Configure corsOrigin, plugin.permissions and alerts.codeHostIntegrationMessaging in site config and repo settings(if you've installed the plugin)

Expected behavior:

Code intelligence hover tooltips and code search is functional while browsing files and viewing pull requests on Bitbucket Server

Actual behavior:

1. Sourcegraph extension/plugin is unavailable in BBS PR view which results in no code intel functionality

Related to #459