docs(kubernetes.md): default to upgrade with install flag set

[dantho281]

Changes the helm install step to do an upgrade, with the install flag set. This way, the same command can be run to later change values

[netlify]

✔️ Deploy Preview for authentik ready!

🔨 Explore the source changes: 3ca4dcf

🔍 Inspect the deploy log: https://app.netlify.com/sites/authentik/deploys/61fd60225dafc10007812e46

😎 Browse the preview: https://deploy-preview-2234--authentik.netlify.app

[codecov]

Codecov Report

Merging #2234 (3ca4dcf) into master (caa382f) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2234      +/-   ##
==========================================
- Coverage   90.23%   90.23%   -0.00%     
==========================================
  Files         447      447              
  Lines       19483    19483              
==========================================
- Hits        17579    17578       -1     
- Misses       1904     1905       +1     

Impacted Files	Coverage Δ
authentik/admin/tasks.py	90.91% <0.00%> (-9.09%)	⬇️
authentik/stages/authenticator_sms/stage.py	90.55% <0.00%> (+5.41%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update caa382f...3ca4dcf. Read the comment docs.