bug: grpc-transcode do not close core.config instance when the plugin is unloaded

[kingluo]

Current Behavior

apisix/apisix/plugins/grpc-transcode.lua

Line 121 in 5f07104

proto.init()

apisix/apisix/plugins/grpc-transcode/proto.lua

Lines 253 to 256 in 5f07104

	protos, err = core.config.new("/protos", {
	automatic = true,
	item_schema = core.schema.proto
	})

This plugin does not define destroy().

config instance of etcd would create a timer to refresh "/protos" resource. We need to close the instance in destroy(), which in turn closes the timer.

Expected Behavior

No response

Error Logs

No response

Steps to Reproduce

curl http://127.0.0.1:9180/apisix/admin/plugins/reload -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT

Environment

• APISIX version (run apisix version): master branch
• Operating system (run uname -a):
• OpenResty / Nginx version (run openresty -V or nginx -V):
• etcd version, if relevant (run curl http://127.0.0.1:9090/v1/server_info):
• APISIX Dashboard version, if relevant:
• Plugin runner version, for issues related to plugin runners:
• LuaRocks version, for installation issues (run luarocks --version):