docs: Adding darkness and brightness examples

[erickzanardo]

Description

Adds two additional examples on the image stories for brightness and darkness changes on images.

Screen.Recording.2023-04-02.at.13.30.29.mov

Checklist

• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

Related Issues

[luanpotter]

Nice!

[spydon]

The blue artifact is not there anymore, but it still produces a white rectangle on the transparent background.

[erickzanardo]

The blue artifact is not there anymore, but it still produces a white rectangle on the transparent background.

@spydon ins't the white rectangle expected? I remember we discussed something about it internally?

[spydon]

@spydon ins't the white rectangle expected? I remember we discussed something about it internally?

That was because previously flame.png had a black background, but it has a transparent background now and a fully transparent color shouldn't be brightened? Maybe that is actually a bug in our code?