bug: upload more than 4096 bytes of grpc proto content and report an error

[tom2nonames]

上传 gRpc proto 内容超过4096个字节报错

Environment

• apisix version : 0.8
• OS: CentOS 7.6

Minimal test code / Steps to reproduce the issue

1. shell cmd

curl http://127.0.0.1:9080/apisix/admin/proto/1 -X PUT -d 'xxxxxxxxx len=4311'

2. error message

{"error_msg":"invalid configuration: property \"content\" validation failed: string too long, expected at most 4096, got 4311"}

3. code

_M.proto = {
    type = "object",
    properties = {
        content = {
            type = "string", minLength = 1, maxLength = 4096
        }
    },
    required = {"content"},
    additionalProperties = false,
}

希望 proto内容的尺寸上限改为一个合理的值.

[nic-chen]

I think we could increase the maxLength to 1M, since ETCD's default max-request-bytes is 1.5M

[membphis]

PR welcome