feat: enable setting a snapshot description for EBS surrogate

[gnought]

Similar to EBS volume, this PR extends the support of setting Snapshot description in EBS surrogate

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[lbajolet-hashicorp]

Hi @gnought,

Thanks for the PR!
I left a small comment on the default value, I think the empty default is good enough that we don't need to generate one if not provided.

Aside from that nit, LGTM! Pre-approving so it is not a blocker later.

[lbajolet-hashicorp]

Note: I see you haven't signed the CLAs, would you be able to do so? If not we won't be able to accept the contribution for legal reasons, sorry about that.

[gnought]

signed CLA and fixes are pushed. Please review. :)

[lbajolet-hashicorp]

Hi @gnought,

I see I misunderstood something in my previous review: the description you added was already the default (which was not changeable in the current state), so we should continue forwarding it, apologies for missing that.
The PR in its previous state was good, no need for the rerolls; given they're separate commits, I'll force-push this branch again without them, and merge as soon as tests go green.

Thanks for the update!