bug: Cannot create a Service with an ID as a string?

[shibingli]

Issue description

Create a Service with a custom ID. Cannot create a Service with an ID as a string

ex:

/apisix/admin/services/{id} //id-> 5ed8b4902b0b28f6b3b4e0a4
/apisix/admin/services/5ed8b4902b0b28f6b3b4e0a4

But if you create Upstream, the ID will be a string

Environment

• apisix version (cmd: apisix version): 1.3
• OS: Linux (Fedora 32 WS)

Minimal test code / Steps to reproduce the issue

1、curl -s http://127.0.0.1:9080/apisix/admin/services/5ed8b4902b0b28f6b3b4e0a4 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -i -X PUT -d '{"desc":"hello world","upstream_id":"5ed77d7ba565f16210f76fcd"}' | awk 'END {print}' | jq .

What's the actual result? (including assertion message & call stack if applicable)

{
"error_msg": "wrong type of service id"
}

What's the expected result?

You can create a resource as an ID of the string type

    if need_id and not tonumber(id) then
        return nil, {error_msg = "wrong type of service id"}
    end

tonumber ?

[moonming]

@shibingli I think it's bug, we should allow string as service ID. Welcome PR