test: synchronizing gherkin specs (#1356)

Co-authored-by: apmmachine <infra-root-apmmachine@elastic.co>

Author: apmmachine

tests/bdd/features/user_agent.feature

@@ -0,0 +1,19 @@
+Feature: Agent Transport User agent Header
+
+ Scenario: Default user-agent
+ Given an agent
+ When service name is not set
+ When service version is not set
+ Then the User-Agent header matches regex '^apm-agent-[a-z]+/[^ ]*'
+
+ Scenario: User-agent with service name only
+ Given an agent
+ When service name is set to 'myService'
+ When service version is not set
+ Then the User-Agent header matches regex '^apm-agent-[a-z]+/[^ ]* \(myService\)'
+
+ Scenario: User-agent with service name and service version
+ Given an agent
+ When service name is set to 'myService'
+ When service version is set to 'v42'
+ Then the User-Agent header matches regex '^apm-agent-[a-z]+/[^ ]* \(myService v42\)'