feat: add findBySlug alias

[IsraelOrtuno]

I have added a convenient method findBySlug to retrieve a model by the saveSlugsTo field configured in the SlugOptions. Works on both HasSlug and HasTranslatableSlug.

[freekmurze]

Thank you!

[francoism90]

@IsraelOrtuno It would be great if you could introduce findBySlugOrFail as well. :)

I've done this before for the prefixed-id package, and it's really helpful when binding this as router parameters.

[IsraelOrtuno]

@IsraelOrtuno It would be great if you could introduce findBySlugOrFail as well. :)

I've done this before for the prefixed-id package, and it's really helpful when binding this as router parameters.

@francoism90 it's indeed useful. Would be interesting to add a whereSlug scope so we could add findBySlug and findBySlugOrFail based on the scope.

Will check on this when I have more time.