[release-1.17] Fix PrivateKeyProvider's problem with proxy-config

[istio-testing]

Manual cherrypick required.

#41761 failed to apply on top of branch "release-1.17":

Applying: add PrivateKeyProviderConfigHash to SecretGen cache key
Using index info to reconstruct a base tree...
M	pilot/pkg/xds/sds.go
Falling back to patching base and 3-way merge...
Auto-merging pilot/pkg/xds/sds.go
CONFLICT (content): Merge conflict in pilot/pkg/xds/sds.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 add PrivateKeyProviderConfigHash to SecretGen cache key
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

[istio-policy-bot]

🚧 This issue or pull request has been closed due to not having had activity from an Istio team member since 2023-02-22. If you feel this issue or pull request deserves attention, please reopen the issue. Please see this wiki page for more information. Thank you for your contributions.

Created by the issue and PR lifecycle manager.