Update and rename self-hosted.mdx to air-gapped.mdx (#1031)

Updating language to align with product roadmap - self-hosted customers
can still access cloud analytics; only airgapped customers will be
offered the grafana analytics solution moving forward.

Author: kelsey-brown

docs/analytics/self-hosted.mdx docs/analytics/air-gapped.mdxdocs/analytics/self-hosted.mdx renamed to docs/analytics/air-gapped.mdx

@@ -1,8 +1,8 @@
-# Sourcegraph Self-Hosted Analytics
+# Sourcegraph Air-gapped Analytics
 
 <Callout type="note">This feature is not yet available. Coming soon.</Callout>
 
-Sourcegraph Self-Hosted Analytics is coming soon! Self-hosted customers can view usage metrics in a locally deployed analytics service built on Grafana.
+Sourcegraph Air-gapped Analytics is coming soon! Air-gapped customers can view usage metrics in a locally deployed analytics service built on Grafana.
 
 This product is in development now. If you would like to learn more, please contact your Sourcegraph representative.