Add nil check after pem.Decode() to prevent crash when public key
PEM data is corrupted or invalid. This fixes a panic at license.go:86
that occurred when block was nil.
Also add test case to verify the fix handles corrupted public keys
gracefully without panicking.
It was a good decision in hindsight to keep the public module as 0.x
because this would have been a breaking change again.
https://mattermost.atlassian.net/browse/MM-53032
```release-note
Changed the Go module path from github.com/mattermost/mattermost-server/server/v8 to github.com/mattermost/mattermost/server/v8.
For the public facing module, it's path is also changed from github.com/mattermost/mattermost-server/server/public to github.com/mattermost/mattermost/server/public
```
* fix fileutils.TestFindFile on MacOS
* introduce model.ExternalServiceEnvironment
* pick license public key from external service env
* pick Stripe public key from external service env
* pick Rudder key from external service env
* configure Sentry DSN from external service env
* always log external_service_environment, Unsetenv
* clear faked BuildEnv, improve logging
* strip out unset GOTAGS
* fix Sentry tests
* simplify to just ServiceEnvironment
* relocate ServiceEnvironment in client config
* initialize CWS URLs based on service environment
* unset rudder key for boards dev
* harden service environment to avoid accidental production
* fix TestSentry again
* fix DEFAULT -> ENTERPRISE
* s/dev/test when naming playbooks rudder key
* simplify boards rudder key switch
* use uniform rudderKey variable names
* retain compatibility with existing pipeline
* reduce to just production/test
* unit test with valid test license
* simplify Playbooks telemetry initialization
* restore dev service environment
* emit ServiceEnvironment when running e2e tests
https://mattermost.atlassian.net/browse/MM-52079
```release-note
We upgrade the module version to 8.0. The new module path is github.com/mattermost-server/server/v8.
```
Co-authored-by: Doug Lauder <wiggin77@warpmail.net>
