fix: Use timeout middleware as the 1st middleware

[thomaspoignant]

Description

Use timeout middleware as the 1st middleware as mentioned here.
It should help when dealing concurrency writing the headers.

@natenho please tell me if you reproduce the bug with the next version.

Closes issue(s)

Resolve #2758

Checklist

• I have tested this code
• I have followed the contributing guide

[netlify]

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

Name	Link
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[thomaspoignant]

@natenho I'll be happy to get your review for this one.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 84.83%. Comparing base (c1eb753) to head (6a30a84).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/relayproxy/api/server.go	75.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2759      +/-   ##
==========================================
- Coverage   84.87%   84.83%   -0.05%     
==========================================
  Files         111      111              
  Lines        5178     5184       +6     
==========================================
+ Hits         4395     4398       +3     
- Misses        620      623       +3     
  Partials      163      163              

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[sonarqubecloud]

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 SonarQube Cloud