Added ability to add relationships to TagsInput

[chrispage1]

Description

This update adds the ability to create a TagsInput field that utilises a BelongsToMany relationship.

For example, a post relationship that has a ->tags() BelongsToMany relationship.

Example usage:

Filament\Forms\Components\TagsInput::make('tags')
    ->relationship(),

By default, it'll look for a BelongsToMany relationship based on the name value.

In its most basic form, if your BelongsToMany relationship matches the name you've given it (in this case 'tags') and the value column in your tags table is name, then there is no further configuration required.

However, if you need to, you can customise the relationship method and the label column that'll be used:

->relationship(relationship: 'testRelationship'), // change the method that'll be called on the model

->relationship(column: 'title'), // change the column that'll be plucked for the tag value.

->relationship('title', 'testRelationship'), // define both values

Visual changes

No visual changes

Functional changes

• [ ✓ ] Code style has been fixed by running the composer cs command.
• [ ✓ ] Changes have been tested to not break existing functionality.
• [ ✓ ] Documentation is up-to-date.