Adds a "how to" for routed nic devices on VMs

[markylaing]

This PR adds a simple tutorial for adding a routed nic device to a virtual machine. With the default gateway configured via cloud init and netplan.

#9529 (comment)

[markylaing]

@ru-fu I'm having a little trouble with this. Firstly make doc-lint is failing with:

doc/.sphinx/.markdownlint/doc-lint.sh
Failed!
.tmp/doc/howto/instances_routed_nic_vm.md:5: MD009 Trailing spaces

Which is a bit odd because I can't see any trailing spaces.

Secondly, the tutorial only appears in the navigation under How-to guides->Instances when I'm on the home page. Where else should I be adding this to the toctree?

[ru-fu]

Thanks Mark!
I'll review later today, but to quickly answer your questions:

doc/.sphinx/.markdownlint/doc-lint.sh
Failed!
.tmp/doc/howto/instances_routed_nic_vm.md:5: MD009 Trailing spaces

The line numbers can be a little off because we're doing some preprocessing on the files. Here it's actually line 4 that has a trailing space.

Secondly, the tutorial only appears in the navigation under How-to guides->Instances when I'm on the home page. Where else should I be adding this to the toctree?

That seems like the correct location, yes. We currently also maintain the "old" navigation, so please also add it to the toctree at the bottom of doc/instances.md (around line 45). Also, for the current navigation, we use alphabetic order, so the new "Add ..." should go between "Access" and "Back up". :)

Oh, and NIC always needs to be capitalised to make the spell checker happy. ;)

[monstermunchkin]

Looks good, but the doc test needs to be fixed.

[ru-fu]

Thanks, looks good to me!
Just a little bit of language nitpicking. ;)

[ru-fu]

Just insisting on some hyphens. 😉

[ru-fu]

Thank you! :)

[tomponline]

Thanks all!