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

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

Additional Context

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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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