Support ACL template policy for Nodes

[vasilij-icabbi]

Feature Description

Automatically populate segment in node resource in ACL. Probably something like "ACL Service Identities" can be reused, or same approach taken. For instance:

node "<node name>" {
    policy = "write"
}

Where <node name> is automatically replaced with actual node name (e.g. consul-1)

Use Case(s)

Consul Server cluster that runs using AWS ASG and least permissive tokens is a requirement. To achieve that, currently need to create custom scripts and handlers.

Discussed here

[blake]

@vasilij-icabbi, Consul 1.8.1 added support for Node Identities in PR #7970, which works similarly to ACL Service Identities.

You can create an agent token with consul acl token create -node-identity=<nodename>:<DC>. The pre-configured ACL policy template listed in the docs will be assigned to the token.