fix: cdk flags outputs empty table when recommended flags are already set

[iankhou]

Fixes #834

Description

DX improvement.

Previously, when the user ran cdk flags but already had all recommended flags configured, an empty table was displayed.

No context here, what does the table mean?

In this change, we added a message to inform the user why they are seeing an empty table. We still print the table to maintain API consistency.

Now the user knows why the table is empty, and is given guidance to display all flags

Testing

Added unit tests for positive and negative cases.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.94%. Comparing base (aef751e) to head (8cfed80).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #836      +/-   ##
==========================================
- Coverage   83.68%   82.94%   -0.74%     
==========================================
  Files          65       65              
  Lines        9547     9554       +7     
  Branches     1137     1122      -15     
==========================================
- Hits         7989     7925      -64     
- Misses       1535     1607      +72     
+ Partials       23       22       -1     

Flag	Coverage Δ
suite.unit	82.94% <100.00%> (-0.74%)	⬇️

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