fix: file exporter path handling

[hoangnv-bkhn]

Description

• Problem:

  • OutputDir in file exporter does not accept non-existent path.
  • If OutputDir is an empty string, the file path will become /{file-name}.json, which would cause it to be treated as an absolute path (instead of a relative path to the current working directory of the process).
    -> This will result in a permission denied error.
  • The documentation recommends that OutputDir should end with /.
    However, the current implementation makes the path look like {OutputDir}//{file-name}.json, resulting in a redundant /.

• The way it was resolved:
  Check the validity of OutputDir and create if necessary

• How to test the change:
  Configure OutputDir with cases: path does not exist, path with trailing /, path is empty string, and observe the results

Closes issue(s)

Resolve #2483

Checklist

• I have tested this code
• I have added unit test to cover this code
• I have updated the documentation (README.md and /website/docs)
• I have followed the contributing guide

[netlify]

✅ Deploy Preview for go-feature-flag-doc-preview canceled.

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🔨 Latest commit	085aebf
🔍 Latest deploy log	https://app.netlify.com/sites/go-feature-flag-doc-preview/deploys/670a4b46a318cd00083c8920

[codecov]

Codecov Report

Attention: Patch coverage is 37.50000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 86.31%. Comparing base (ed39a6e) to head (bbe6500).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
exporter/fileexporter/exporter.go	37.50%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2498      +/-   ##
==========================================
- Coverage   86.48%   86.31%   -0.18%     
==========================================
  Files         100      100              
  Lines        3544     3551       +7     
==========================================
  Hits         3065     3065              
- Misses        352      355       +3     
- Partials      127      131       +4     

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[hoangnv-bkhn]

To edit docs, besides changing the content of the .md files in /website/docs, what else do I need to do?
It seems that the docs on the website are not updated according to what I edited

[thomaspoignant]

@hoangnv-bkhn Thanks for your pull request, this makes the file exporter way better than it was before 🙇.
I have added a test in the case we have no outputDir.

Everything else is really great.
I will merge it soon and it will be available in the next release.

[thomaspoignant]

I have added a test case for when we have no outputDir.

[thomaspoignant]

It seems that the docs on the website are not updated according to what I edited

Oh sorry I forgot to address this one.
The doc is versioned this is why you don't see the change, but if you add /next after /docs you are able to see the next version of the doc after the release (ex: https://gofeatureflag.org/docs/next).

In the preview for this PR it will be in https://deploy-preview-2498--go-feature-flag-doc-preview.netlify.app/docs/next

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud