Add SOCKS proxy support

[hkobayash]

It allows you to proxy the requests to the MongoDB server through a SOCKS proxy, in case the MongoDB server cannot be reached directly.

[henryjustinserrano]

Hello, any idea when this PR might get looked at?

[ITMonta]

@hkobayash @henryjustinserrano , Sorry for the delay and thanks for the contribution. Version : v0.1.6 of the provider is published

[timwisbauer-contsec]

Would it be possible to also allow configuring the proxy via the provider, similar to how this mysql provider works? That way you could use a SOCKS proxy just for this provider and not all providers.

Configuring the provider: https://github.com/petoju/terraform-provider-mysql/blob/master/mysql/provider.go#L85-L92 Constructing the dialer: https://github.com/petoju/terraform-provider-mysql/blob/master/mysql/provider.go#L227-L245

[ITMonta]

we will work on that :)

[ITMonta]

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