Remove the deprecated `key_algorithm` argument from `*_cert` resources

[detro]

Terraform CLI and Provider Versions

0.12

Use Cases or Problem Statement

Context: #173

The Algorithm of the Private Key algorithm is inferred from the Key itself as of 3.2.0.
We have deprecated it in 3.2.0: this issue is about removing it, and replacing it with a Computed value that plays an "informative" role.

Proposal

Fields key_algorithm are removed after deprecation in 3.2.0.
Also testing setup to aid the deprecation should be removed.

How much impact is this issue causing?

Low

Additional Information

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[github-actions]

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