feat(image-sharp): add trim option

[cpboyd]

Description

Add the @lovell/sharp trim option (and standardize fit & background from fluid to fixed).

I was trying different sharp options with a list of video screenshots (currently using fixed()), some of which have black bars, and saw that sharp offered a trim option.

Further, the fit and background settings weren't available on fixed.

Note: My original plan was to have it accept either a boolean or int, with true representing the sharp default threshold. (currently 10)

Unfortunately, per graphql/graphql-spec#488, GraphQL doesn't accept union types as inputs currently. GraphQLInt coalesces true to 1 and false to 0 (0 is an invalid threshold value, so it's still OK to use to disable the setting)

Related Issues

[freiksenet]

I don't think there is much value to split the argument into a boolean and a float, it'd be pretty easy for the user to pass trim default value as an argument, so there is no need to complicate the API further.

[cpboyd]

@freiksenet I made the requested changes, but squashed the prior commits before pushing the new changes which may have interrupted the normal review workflow.

Do I need to do make any other changes?