fix: add default port to enable SENTINEL_PORT environment

[drivebyer]

Description

Fixes #995

When a user uses an old Redis image that does not have SENTINEL_PORT set as the default environment variable, we must configure SENTINEL_PORT to 26379 in the operator. Otherwise, the Sentinel probe will fail.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• Tests have been added/modified and all tests pass.
• Functionality/bugs have been confirmed to be unchanged or fixed.
• I have performed a self-review of my own code.
• Documentation has been updated or added where necessary.

Additional Context

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 45.85%. Comparing base (d121d86) to head (6c8efc0).
Report is 78 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #999       +/-   ##
===========================================
+ Coverage   35.20%   45.85%   +10.64%     
===========================================
  Files          19       20        +1     
  Lines        3213     2687      -526     
===========================================
+ Hits         1131     1232      +101     
+ Misses       2015     1380      -635     
- Partials       67       75        +8     

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