feat: add support for json credentials (#271)

examples/resources/boundary_credential_json/import.sh

@@ -0,0 +1 @@
+terraform import boundary_credential_json.example_json <my-id>

examples/resources/boundary_credential_json/resource.tf

@@ -0,0 +1,27 @@
+resource "boundary_scope" "org" {
+  name                     = "organization_one"
+  description              = "global scope"
+  scope_id                 = "global"
+  auto_create_admin_role   = true
+  auto_create_default_role = true
+}
+
+resource "boundary_scope" "project" {
+  name                   = "project_one"
+  description            = "My first scope!"
+  scope_id               = boundary_scope.org.id
+  auto_create_admin_role = true
+}
+
+resource "boundary_credential_store_static" "example" {
+  name        = "example_static_credential_store"
+  description = "My first static credential store!"
+  scope_id    = boundary_scope.project.id
+}
+
+resource "boundary_credential_json" "example" {
+  name                = "example_json"
+  description         = "My first json credential!"
+  credential_store_id = boundary_credential_store_static.example.id
+  object              = file("~/object.json") # change to valid json file
+}