Allow identity blocks in sidecar_task blocks

[seanamos]

Proposal

Allow the use of identity blocks in sidecar_task blocks.

This is similar in nature to #17987 .

Use-cases

Allow the injection of AWS identities into terminating gateways that invoke lambdas.

Attempted Solutions

It is possible the suggestion at #17987 (comment) would also work for this, that is to construct the job json in it's entirety manually and submit it. I have not tested this yet.

An easier to implement workaround is to add permissions to the EC2 IAM role/policy, but this is undesirable.

If #17987 were implemented and one has a Vault AWS secret backend, that could also work as an alternative solution.

[tgross]

Hi @seanamos! This seems like a reasonable idea. I'll mark it for roadmapping, but I'm not sure when we'd get to this. You may want to look into deploying the gateway job as a standalone task, similar to what we've demonstrated in https://github.com/hashicorp-guides/consul-api-gateway-on-nomad