MM-23568: Add rudder to server diagnostics. (#14151)

* MM-23568: Add rudder to server diagnostics.

* Add unit test.

* Go mod tidy.

* CSP Header fix.

* Fix review comments.

* Update web/handlers.go

Co-Authored-By: Jesse Hallam <jesse.hallam@gmail.com>

* Partially address review comments.

* fix tests.

* Finish implementing review suggestions and then fixing tests.

* Fix CSP Header tests.

Co-authored-by: Jesse Hallam <jesse.hallam@gmail.com>

vendor/modules.txt

@@ -289,6 +289,9 @@ github.com/prometheus/procfs/internal/util
 # github.com/rs/cors v1.7.0
 ## explicit
 github.com/rs/cors
+# github.com/rudderlabs/analytics-go v3.1.0+incompatible
+## explicit
+github.com/rudderlabs/analytics-go
 # github.com/russellhaering/goxmldsig v0.0.0-20180430223755-7acd5e4a6ef7
 ## explicit
 github.com/russellhaering/goxmldsig