Add image variation implementation and fix #149

[itegel]

1. Fix issue The CreateEditImage API should have an optional Mask parameter. #149
2. Add image variation implementation according to
   https://platform.openai.com/docs/api-reference/images/create-variation

[sashabaranov]

@itegel there's some issue with CI workflow, could you please re-base on the master branch?

[codecov]

Codecov Report

Merging #153 (f1ca475) into master (f4a6a99) will increase coverage by 0.17%.
The diff coverage is 58.33%.

@@            Coverage Diff             @@
##           master     #153      +/-   ##
==========================================
+ Coverage   50.19%   50.36%   +0.17%     
==========================================
  Files          16       16              
  Lines         516      548      +32     
==========================================
+ Hits          259      276      +17     
- Misses        201      211      +10     
- Partials       56       61       +5     

Impacted Files	Coverage Δ
image.go	48.27% <58.33%> (+2.82%)	⬆️

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[itegel]

@itegel there's some issue with CI workflow, could you please re-base on the master branch?
Hi,

1. I`ve fixed the lint problem.
2. The Codeball problem seems to be related to repo permissions. Here is the suggestion from the codeball owner, you may need to install "Codeball AI Writer" on the repo. I do not know to fix it, please help me

/*
Forks and public repositories
GitHub does not offer (and reasonably so) a way for Pull Requests from a fork to a public repository to run with "write" permissions to the parent repository.
If you want to use Codeball on a public repository, install the "Codeball AI Writer" app on the parent repository. This allows the Codeball Action to use the permissions from the app as a fallback if the action is running without write permissions.
*/

[sashabaranov]

looks good, thank you!