Add SONiC testbed docs

[matofeder]

• This PR adds a tutorial that walks you through setting up and configuring a basic testbed environment in the GNS3 simulation platform. The setup includes three SONiC switches (Spline, Leaf1, Leaf2) with community images and two PCs connected to Leaf1 and Leaf2.
  • The guide also covers a basic BGP L3 underlay configuration using FRR.
• This PR moves some general SONiC docs into a separate file under the docs directory

@scoopex I just wanted to push my test environment docs to the repo, as I always prefer to have the possibility to develop things locally. Netbox, ansible thing is ongoing and I'm testing it with the provided SONiC testbed env.

relates to SovereignCloudStack/issues#538

[berendt]

I think it makes more sense to add this docs to https://github.com/sovereigncloudstack/docs ?

[matofeder]

I think it makes more sense to add this docs to https://github.com/sovereigncloudstack/docs ?

I agree that landscape-related docs should be visible at https://docs.scs.community/

AFAIK The recommended way is to reference the repository docs files in the SCS docs repository. See e.g. SovereignCloudStack/docs#144

So we could create a landscape section in the SCS docs and reference the pages we would like to see in the official SCS docs page.

[scoopex]

I think it makes more sense to add this docs to https://github.com/sovereigncloudstack/docs ?

Sure, lets discuss that with @maxwolfs to have a SONiC Section in the documentation.

[scoopex]

LGTM