Add pipeline source to custom CI_JOB_JWT claims

Changelog: added

doc/ci/examples/authenticating-with-hashicorp-vault/index.md

@@ -50,6 +50,7 @@ The JWT's payload looks like this:
   "user_login": "myuser"                         # GitLab @username
   "user_email": "myuser@example.com",            # Email of the user executing the job
   "pipeline_id": "1212",                         #
+  "pipeline_source": "web",                      # Pipeline source, see: https://docs.gitlab.com/ee/ci/yaml/#common-if-clauses-for-rules
   "job_id": "1212",                              #
   "ref": "auto-deploy-2020-04-01",               # Git ref for this job
   "ref_type": "branch",                          # Git ref type, branch or tag

lib/gitlab/ci/jwt.rb

@@ -54,6 +54,7 @@ module Gitlab
           user_login: user&.username,
           user_email: user&.email,
           pipeline_id: build.pipeline.id.to_s,
+          pipeline_source: build.pipeline.source.to_s,
           job_id: build.id.to_s,
           ref: source_ref,
           ref_type: ref_type,

spec/lib/gitlab/ci/jwt_spec.rb

@@ -42,6 +42,7 @@ RSpec.describe Gitlab::Ci::Jwt do
         expect(payload[:user_email]).to eq(user.email)
         expect(payload[:user_login]).to eq(user.username)
         expect(payload[:pipeline_id]).to eq(pipeline.id.to_s)
+        expect(payload[:pipeline_source]).to eq(pipeline.source.to_s)
         expect(payload[:job_id]).to eq(build.id.to_s)
         expect(payload[:ref]).to eq(pipeline.source_ref)
         expect(payload[:ref_protected]).to eq(build.protected.to_s)