feat: adds SSH support + tagging + upgrades ssm-agent 1.0

[Gowiem]

what

• Adds SSH support
• Adds ability to override the primary tag that the auth key is generated with
• Adds ability to add additional tags to subnet router machines
• Upgrades ssm-agent module to v1.0.0 (not yet released, but will be via: feat: roll instances + modify ASG sizes + add aqua terraform-aws-ssm-agent#20)

why

• SSH support was requested in Support Tailscale SSH #10 + it was useful for us on a project when testing Transit Gateways
• See requested changes in Error: requested tags [tag:prod] are invalid or not permitted #9 regarding the tag the auth key is created with. Tailscale is pretty annoying about "tags" so we want that to be configurable to whatever the consumer created their OAuth client with.
• More tags on the machine mean the ability to further specify / group machines.
• Upgrades to the latest ssm-agent module which now will roll the Tailscale instances when new updates are made to the Launch Template

references

• Closes Support Tailscale SSH #10
• Closes Error: requested tags [tag:prod] are invalid or not permitted #9

[kevcube]

@Gowiem Why remove instance_count?

Edit: oh I see now in ssm-agent -- I'll review that first

[gberenice]

I'm confused about this change. I assume something could be changed in Tailscale auth/tagging logic, but previously the machine was tagged when authenticated with the pre-authentication Tailnet key, see the comment.
I get why we might want to concat context.tf tags + additional tags provided by a user, but I don't get why we need to add this flag and use different tags for the key and for up command.

[Gowiem]

To recap the conversation we had over a call for history purposes:

1. We weren't including the primary_tag in this list, which was a mistake on my end. I've now fixed that in a recent push.
2. We're going to keep this --advertise-tags bit here because it's useful to be explicit since Tailscale is confusing af at times.

[gberenice]

What I was going to update here (and successfully forgot to complete 😑) is to redo the example without referencing to context.tf (maybe worth leaving it commented for the users who utilize this pattern). Do you want me to add this to your branch? Or you'll update it by yourself?

[Gowiem]

@gberenice Hm -- I'm glad you're thinking of this as I always forget to update the example. I think what I'll do is update the readme for the two use-cases: 1) passing primary_tag and 2) passing in context.tf label elements to create the module.this.id

[gberenice]

Looks good! Thanks for updating the tags naming in the last iteration - it's definitely easier to understand 👍