Enable injecting middlewares into the Firebase API client

[l-alexandrov]

Description

It makes possible adding a Guzzle middleware to the Guzzle HTTP client. This feature was recently introduced in the SDK in version 7.3.0

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works
• I have made corresponding changes to the documentation

[codecov]

Codecov Report

Merging #187 (5d680bf) into main (ff02dbd) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main     #187      +/-   ##
============================================
+ Coverage     98.38%   98.41%   +0.02%     
- Complexity       46       47       +1     
============================================
  Files             3        3              
  Lines           124      126       +2     
============================================
+ Hits            122      124       +2     
  Misses            2        2              

Impacted Files	Coverage Δ
src/FirebaseProjectManager.php	96.87% <100.00%> (+0.10%)	⬆️

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[jeromegamez]

Thanks! 🙏🏻