Documentation/integrations: add PHP v3 client

[ouqiang]

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[hexfusion]

@ouqiang can you add that the client uses gRPC gateway please. Thanks!

[ouqiang]

ok

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[hexfusion]

@ouqiang kind ping, if you can update commit and rebase I will get this merged. Thanks!

[ouqiang]

Sorry, I can't currently provide a client using a gRPC gateway, I think using HTTP is more suitable for PHP

[hexfusion]

Sorry, I can't currently provide a client using a gRPC gateway, I think using HTTP is more suitable for PHP

@ouqiang your solution uses the v3 HTTP API which is exposed by the gRPC gateway. So all that I need is for you to change your commit from

[ouqiang/etcd-php](https://github.com/ouqiang/etcd-php) - Client for v3

to

[ouqiang/etcd-php](https://github.com/ouqiang/etcd-php) - Client for v3 gRPC gateway

So that people can understand this.

Thanks!