chore: support PEM format cert for service principal + cert auth

[bowen5]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Currently SP+Cert auth only support PFX format. This PR is to add:

• Change to use azidentity.ParseCertificates instead of ``adal.DecodePfxCertificateData`, to parse both PEM and PFX format certs.
• Add logic to find expected public cert file when multi public cert bag provided, by referencing https://github.com/Azure/go-autorest/blob/main/autorest/adal/persist.go#L110.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Service principal with cert auth supports PEM format cert.

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

Hi @bowen5. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[feiskyer]

/ok-to-test

[feiskyer]

/kind feature

[feiskyer]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bowen5, feiskyer

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• OWNERS [feiskyer]

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[MartinForReal]

/cherrypick release-1.30

[k8s-infra-cherrypick-robot]

@MartinForReal: #6601 failed to apply on top of branch "release-1.30":

Applying: update
.git/rebase-apply/patch:262: trailing whitespace.
    localKeyID: 01 00 00 00 
.git/rebase-apply/patch:266: trailing whitespace.
    X509v3 Key Usage: 10 
.git/rebase-apply/patch:317: trailing whitespace.
    localKeyID: 01 00 00 00 
.git/rebase-apply/patch:347: trailing whitespace.
    localKeyID: 01 00 00 00 
.git/rebase-apply/patch:351: trailing whitespace.
    X509v3 Key Usage: 10 
warning: 5 lines add whitespace errors.
Using index info to reconstruct a base tree...
M	pkg/provider/config/azure_auth.go
M	pkg/provider/config/azure_auth_test.go
Falling back to patching base and 3-way merge...
Auto-merging pkg/provider/config/azure_auth_test.go
CONFLICT (content): Merge conflict in pkg/provider/config/azure_auth_test.go
Auto-merging pkg/provider/config/azure_auth.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
Patch failed at 0001 update

In response to this:

/cherrypick release-1.30

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.