Keep user and cluster name when add kubeconfig

[astraw99]

Fixes: #351

To keep the user and cluster name when add kubeconfig.
When user or cluster name already exists, will add a hash suffix, e.g. cls-orig-gtch2cf96d user-orig-gtch2cf96d.

Also updated test cases to check it correctly.

[gitguardian]

⚠️ GitGuardian has uncovered 2 secrets following the scan of your pull request.

Please consider investigating the findings and remediating the incidents. Failure to do so may lead to compromising the associated services or software components.

🔎 Detected hardcoded secrets in your pull request

GitGuardian id	Secret	Commit	Filename
-	Generic High Entropy Secret	fc07952	cmd/add_test.go	View secret
-	Generic High Entropy Secret	fc07952	cmd/add_test.go	View secret

🛠 Guidelines to remediate hardcoded secrets

1. Understand the implications of revoking this secret by investigating where it is used in your code.
2. Replace and store your secrets safely. Learn here the best practices.
3. Revoke and rotate these secrets.
4. If possible, rewrite git history. Rewriting git history is not a trivial act. You might completely break other contributing developers' workflow and you risk accidentally deleting legitimate data.

To avoid such incidents in the future consider

• following these best practices for managing and storing secrets including API keys and other credentials
• install secret detection on pre-commit to catch secret before it leaves your machine and ease remediation.

---

<sup>🦉 GitGuardian detects secrets in your source code to help developers and security teams secure the modern development process. You are seeing this because you or someone else with access to this repository has authorized GitGuardian to scan your pull request.

Our GitHub checks need improvements? Share your feedbacks!</sup>

[codecov]

Codecov Report

Merging #536 (fc07952) into master (c32d19e) will increase coverage by 1.35%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #536      +/-   ##
==========================================
+ Coverage   11.43%   12.79%   +1.35%     
==========================================
  Files          19       19              
  Lines        1862     1891      +29     
==========================================
+ Hits          213      242      +29     
  Misses       1632     1632              
  Partials       17       17              

Flag	Coverage Δ
unittests	12.79% <100.00%> (+1.35%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/add.go	38.51% <100.00%> (+14.98%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[sunny0826]

Thanks, I haven't had time to deal with this.

[sunny0826]

Only a small change is required.

[sunny0826]

LGTM