feat: Add title to publish-post, implement for Pinterest

[jnv]

Description

Pinterest is one of the few social medias where the post can contain a title. Unfortunately we don't have a field to accomodate for that, so I added a new field to the social-media/publish-post and bumped minor version accordingly. The field is ignored by other maps.

Motivation and Context

Requested by users. Publishing to Pinterest without a possibility to set the title is kinda useless.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] I have read the CONTRIBUTING document.
• [x] I haven't repeated the code. (DRY)
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.