Declare a maximum length for contact category machine name

Problem/Motivation

Possibly a follow-up to #1709960: declare a maximum length for entity and bundle machine names, where entity bundle machine names limit length to 32 characters. Contact category will throw the following exception when longer than 32 characters.

Proposed resolution

Add a maxlength to machine_name.

User interface changes

Alter machine name field only allow 32 characters.

API changes

None.

Steps to Reproduce

1. Enable the contact module
2. At Home > Administration > Structure > Contact form categories > Add category (admin/structure/contact/add)
3. Add a label with a very long value like "ABCDEFGHIJKLM NOPQRSTUVWXYZ abcdefghijklm nopqrstuvwxyz 1234567890 ABCDEFGHIJKLM NOPQRSTUVWXYZ abcdefghijklm nopqrstuvwxyz 1234567890 ABCDEFGHIJKLM NOPQRSTUVWXYZ abcdefghijklm nopqrstuvwxyz 1234567890 ABCDEFGHIJKLM NOPQRSTUVWXYZ abcdefghijklm nopqrstuvwxyz 1234567890 ABCDEFGHIJKLM NOPQRSTUVWXYZ abcdefghijklm nopqrstuvwxyz 1234567890 ABCDEFGHIJKLM NOPQRSTUVWXYZ abcdefghijklm nopqrstuvwxyz 1234567890".
4. Add a sample value to the required recipients field like "webmaster@example.com"
5. Click save
6. Site will return the following exception.

Drupal\Core\Config\Entity\Exception\ConfigEntityIdLengthException: Attempt to create a bundle with an ID longer than 32 characters: abcdefghijklm_nopqrstuvwxyz_abcdabcdefghijklm_nopqrstuvwxyz_abcd. in Drupal\Core\Entity\Entity->preSave() (line 347 of core/lib/Drupal/Core/Entity/Entity.php).