Add ability to transform color space

[Anticom]

It would be great if we were able to transform the color space of an image.

My brief research on driver support yielded, that this would potentially be possible using Imagick and Vips drivers. GD seems to not support this.

Please share your thoughts, I am happy to provide a PR.

[Anticom]

After thinking about this a bit more and looking more into the internals of your related spatie/media-library package, it occured to me, that it would also be a valid and maybe more desirable approach to add a MediaWillBeAdded / MediaIsBeingAdded / etc. event that is being emitted after the image is available on a local disk (typically in the temporary directory I assume) but before it has finished being processed (as in before it has been copied to the media library's final destination and the MediaHasBeenAdded event has been emitted).
This could probably also go into the Filesystem.

Risks / Limitations / Challenges I can think of with this approach:

1. How are conversions being handled? Do they get a dedicated event, no event at all or the unified event an additional flag? etc.
2. Listeners MUST run in sync if they want to modify the file. Additionally they probably also MUST write back to the same file path to not add additional complexity.
3. This approach does not enable consumers of this package. However this package also is not concerned with handling the entire process from start to finish.
4. Maybe it is the philosophy of spatie/laravel-medialibrary to never change the original image since we have conversions for this. Adding a way to hook into this process would allow to break this philosophy.

Why I think this approach is more desirable though:

Besides my need to have this ability in conjunction with spatie/laravel-medialibrary, this could totally be achieved manually with something along the lines of

$image->image()-> transformImageColorspace(Imagick::COLORSPACE_SRGB);

Moreover by adding an api to this image, we would only be able to conveniently manipulate the color space for conversions when working with spatie/laravel-medialibrary but not for the original image, as far as I can tell.

Conclusion:

While it certainly wouldn't hurt to add the respective api to this package, it would merely enable adding a listener to ConversionWillStartEvent to perform this manipulation on conversions. Listening on MediaHasBeenAdded to copy the file again, open it up using an image driver, performing the manipulation and writing it back to its temporary file in order to move it back to its final destination where it came from seems overly convoluted and way more error prone.
Hence I suggest actually doing both things: Add the respective api to this package and an additional event to the medialibrary package.
This way users of this package get a new feature working for most drivers and users of the medialibrary gain the ability to apply this manipulation (among other things) in a convenient manner.
In case you want to continue to guarantee, that the original file can not be altered by only using the package's existing apis, it would still help to get this api added to this package so we can at least perform that manipulation when generating a conversion.

---

Let me know whether I should transfer parts of this discussion to spatie/laravel-medialibrary since we're interleaving concerns here.