set max_length for entity_import_status base fields

Problem/Motivation

Most of the fields for the entity_import_status entity are created in the DB as varchar(255):

  `entity_id` varchar(255) DEFAULT NULL,
  `entity_uuid` varchar(255) DEFAULT NULL,
  `entity_type_id` varchar(255) DEFAULT NULL,
  `entity_bundle` varchar(255) DEFAULT NULL,
  `remote_website` varchar(255) DEFAULT NULL,
  `channel_id` varchar(255) DEFAULT NULL,
  `last_import` int DEFAULT NULL,
  `policy` varchar(255) DEFAULT NULL,

This is more space than they need -- the uuid, and anything that's a config entity ID has a maximum that's much shorter than that.

Steps to reproduce

Proposed resolution

Set the max_length on the fields.

Remaining tasks

User interface changes

API changes

Data model changes