Issue #3555316: Fix incorrect admin_permission for TemplateMap entity

Problem / Background

The mailchimp_transactional_template entity currently defines an incorrect admin_permission in its entity annotation.

In the file: TemplateMap.php

the annotation currently says:

admin_permission = "administer mailchimp_transactional" However, the module actually defines the permission as: administer mailchimp transactional templates

As a result, even users with the intended permission cannot access the admin route /admin/config/services/mailchimp_transactional/templates, leading to 403 Access denied errors.

Proposed fix: admin_permission = "administer mailchimp transactional templates"