added support for Attachments (aka Embedddings)

[Johnlon]

🤔 What's changed?

The cucumber and events formatters support the inclusion of Attachments.

The proposed API is demonstrated in the tests as ...

func stepWithAttachment(ctx context.Context) (context.Context, error) {
    ctxOut := godog.Attach(ctx,
	godog.Attachment{Body: []byte("TheData1"), FileName: "TheFilename1", MediaType: "text/plain"},
	godog.Attachment{Body: []byte("TheData2"), FileName: "TheFilename2", MediaType: "text/plain"},
    )

    return ctxOut, nil
}

⚡️ What's your motivation?

#617

Want support for Attachments from steps.
This PR proposes to use the context.Context object as a means to attach content from the step.

🏷️ What kind of change is this?

• ⚡ New feature (non-breaking change which adds new behaviour)

♻️ Anything particular you want feedback on?

This change involves minimal changes to patterns of use of godog API's.

I added tests for the cuke and events formats but the coverage isn't being recorded even on some lines I didn't modify.

fmt_output_test.go now has a normalise() fn that eliminates some extraneous diffs in the actual/expected files such as line endings and also line numbers so that the tests are easier to maintain and cross platform,

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• [ x] I've changed the behaviour of the code
  • [ x] I have added/updated tests to cover my changes.
• [ x] My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

[codecov]

Codecov Report

Attention: Patch coverage is 88.70968% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 79.69%. Comparing base (153db4e) to head (2d66c72).
Report is 8 commits behind head on main.

❗ Current head 2d66c72 differs from pull request most recent head a8f193f

Please upload reports for the commit a8f193f to get more accurate results.

Files	Patch %	Lines
suite.go	81.25%	5 Missing and 1 partial ⚠️
internal/models/results.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #623      +/-   ##
==========================================
- Coverage   83.21%   79.69%   -3.52%     
==========================================
  Files          28       40      +12     
  Lines        3413     3113     -300     
==========================================
- Hits         2840     2481     -359     
- Misses        458      513      +55     
- Partials      115      119       +4     

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