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>

go.sum

@@ -282,7 +282,6 @@ github.com/mattermost/gosaml2 v0.3.2 h1:kq2dY5qUe6fPPHra171GVlgo+ycBsEog0gZMetxL
 github.com/mattermost/gosaml2 v0.3.2/go.mod h1:Z429EIOiEi9kbq6yHoApfzlcXpa6dzRDc6pO+Vy2Ksk=
 github.com/mattermost/ldap v0.0.0-20191128190019-9f62ba4b8d4d h1:2DV7VIlEv6J5R5o6tUcb3ZMKJYeeZuWZL7Rv1m23TgQ=
 github.com/mattermost/ldap v0.0.0-20191128190019-9f62ba4b8d4d/go.mod h1:HLbgMEI5K131jpxGazJ97AxfPDt31osq36YS1oxFQPQ=
-github.com/mattermost/mattermost-server v5.11.1+incompatible h1:LPzKY0+2Tic/ik67qIg6VrydRCgxNXZQXOeaiJ2rMBY=
 github.com/mattermost/rsc v0.0.0-20160330161541-bbaefb05eaa0 h1:G9tL6JXRBMzjuD1kkBtcnd42kUiT6QDwxfFYu7adM6o=
 github.com/mattermost/rsc v0.0.0-20160330161541-bbaefb05eaa0/go.mod h1:nV5bfVpT//+B1RPD2JvRnxbkLmJEYXmRaaVl15fsXjs=
 github.com/mattermost/viper v1.0.4 h1:cMYOz4PhguscGSPxrSokUtib5HrG4gCpiUh27wyA3d0=
@@ -412,6 +411,8 @@ github.com/rogpeppe/fastuuid v0.0.0-20150106093220-6724a57986af/go.mod h1:XWv6So
 github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
 github.com/rs/cors v1.7.0 h1:+88SsELBHx5r+hZ8TCkggzSstaWNbDvThkVK8H6f9ik=
 github.com/rs/cors v1.7.0/go.mod h1:gFx+x8UowdsKA9AchylcLynDq+nNFfI8FkUZdN/jGCU=
+github.com/rudderlabs/analytics-go v3.1.0+incompatible h1:raJgBJMxxnCe9CWHL1zJq4rccap4yG7lvk4Fs6B7v+o=
+github.com/rudderlabs/analytics-go v3.1.0+incompatible/go.mod h1:LF8/ty9kUX4PTY3l5c97K3nZZaX5Hwsvt+NBaRL/f30=
 github.com/russellhaering/goxmldsig v0.0.0-20180430223755-7acd5e4a6ef7 h1:J4AOUcOh/t1XbQcJfkEqhzgvMJ2tDxdCVvmHxW5QXao=
 github.com/russellhaering/goxmldsig v0.0.0-20180430223755-7acd5e4a6ef7/go.mod h1:Oz4y6ImuOQZxynhbSXk7btjEfNBtGlj2dcaOvXl2FSM=
 github.com/russross/blackfriday v1.5.2/go.mod h1:JO/DiYxRf+HjHt06OyowR9PTA263kcR/rfWxYHBV53g=