[doc] Fix minUnavailable typo in PDB

[frivoire]

Hello,

This is a simple typo in the description of the PDB:
The minUnavailable concept doesn't exists in K8S, it's either minAvailable or maxUnavailable.

Thus this PR to fix this error everywhere I've grep found it ;)

[prodsecmachine]

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[github-actions]

🔍 Preview links for changed docs

• docs/reference/api-reference/3_0_0.md
• docs/reference/api-reference/3_1_0.md
• docs/reference/api-reference/3_2_0.md
• docs/reference/api-reference/main.md