Sunset Datadog

Created by: daxmc99

Based on internal feedback we plan to return to our previous observability solutions and led the decision by lead by #wg-observability

Places we need to remove Datadog from:

• Cloud Helm chart https://sourcegraph.com/search?q=context:global+datadog+repo:%5Egithub%5C.com/sourcegraph/.*cloud*%24+&patternType=literal
• Possibly some places in our internal codebase (if they are not flagged off) https://sourcegraph.com/search?q=context:global+repo:%5Egithub%5C.com/sourcegraph/sourcegraph%24+datadog&patternType=literal
• Possible revert of https://github.com/sourcegraph/sourcegraph/pull/34063 (or check that is feature-flagged)