This endpoint will return the customer tags stored in Rejoiner.
You can use either the Rejoiner Customer ID or the customer's email address.
GET /customers/CUSTOMER_ID/tags/
GET /customers/tags/by_email/?email=CUSTOMER_EMAIL
{
"customer_tags": [
"foo",
"bar"
],
"site_tags": [
"spam",
"ham",
"foo",
"bar
]
}