CDPT-1076 Add theme support for title-tag.

[EarthlingDavey]

The current theme had issues setting the <title> element on the homepage.

Adding theme support for title-tag is the recommended approach for fixing the issue.

Reference:

• https://developer.wordpress.org/reference/functions/add_theme_support/
• https://stackoverflow.com/a/37223205/6671505
• https://wordpress.stackexchange.com/questions/305353/cant-change-the-title-tag-with-wp-title-filter