Report grape gem version in environment metadata (#1534)

Grape is a supported integration (loaded via Appsignal.load(:grape)) but was
missing from the SUPPORTED_GEMS list that drives environment gem-version
reporting. As a result, Grape apps never reported a ruby_grape_version, making
Grape adoption invisible in telemetry (unlike its sibling loader frameworks
hanami, sinatra, and padrino, which are all in the list). Add grape so its
version is reported like the others.

Author: serenachou

.changesets/report-grape-in-supported-gems.md

@@ -0,0 +1,6 @@
+---
+bump: patch
+type: add
+---
+
+Report the `grape` gem version in the environment metadata. For more information, see [our environment metadata docs](https://docs.appsignal.com/application/environment-metadata).

lib/appsignal/environment.rb

@@ -87,6 +87,7 @@ def self.report(key)
       elasticsearch
       excon
       faraday
+      grape
       gvltools
       hanami
       hiredis