Add identity details to error messages

[horjulf]

This adds more detail to the identity data resources error messages, making it possible to identify which entry is erroring when using for_each or count resources.

Before:

Error: no Identity Entity found

  on main.tf line 9, in data "vault_identity_entity" "user":
   9: data "vault_identity_entity" "user" {

After:

Error: no Identity Entity found 'map[name:john@doe.com]'

  on main.tf line 9, in data "vault_identity_entity" "user":
   9: data "vault_identity_entity" "user" {

[hashicorp-cla]

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