feat(admin-api): add gateway edition info to the endpoint / (#12097)

This commit is the follow-up change to the PR #12045,
since the the edition info is still useful to the kong manager, we choose to
introduce the gateway edition information in the response of the `/` endpoint.

Fix FTI-5557

changelog/unreleased/kong/add-gateway-edition-to-root-endpoint-admin-api.yml

@@ -0,0 +1,3 @@
+message: add gateway edition to the root endpoint of the admin api
+type: feature
+scope: Admin API

kong/api/routes/kong.lua

@@ -106,6 +106,7 @@ return {
       return kong.response.exit(200, {
         tagline = tagline,
         version = version,
+        edition = meta._VERSION:match("enterprise") and "enterprise" or "community",
         hostname = knode.get_hostname(),
         node_id = node_id,
         timers = {

spec/02-integration/04-admin_api/02-kong_routes_spec.lua

@@ -69,14 +69,15 @@ describe("Admin API - Kong routes with strategy #" .. strategy, function()
       assert.not_nil(res.headers["X-Kong-Admin-Latency"])
     end)
 
-    it("returns Kong's version number and tagline", function()
+    it("returns Kong's version number, edition info and tagline", function()
       local res = assert(client:send {
         method = "GET",
         path = "/"
       })
       local body = assert.res_status(200, res)
       local json = cjson.decode(body)
       assert.equal(meta._VERSION, json.version)
+      assert.equal(meta._VERSION:match("enterprise") and "enterprise" or "community", json.edition)
       assert.equal("Welcome to kong", json.tagline)
     end)
     it("returns a UUID as the node_id", function()