fix: restore IRSA support for S3 asset store

[chris-at-tyler]

Summary

• add an explicit AWSSDK.SecurityToken dependency so IRSA/web-identity credentials work again in the S3 asset store
• use a real seekable temp stream for non-seekable S3 uploads instead of SeekFakerStream
• avoid masking the original S3 startup failure behind retry rewind errors

Validation

• reproduced the startup failure with 7.22.0+ in EKS using S3 + IRSA
• validated the patched image in isolated QA and sandbox pods
• validated the patched image in the sandbox live deployment

Related

• Squidex/squidex issue: Regression: 7.22.0+ fails to start with S3 when AWS credentials are resolved via web identity because AWSSDK.SecurityToken is missing and retry is masked by SeekFakerStream squidex#1309

[SebastianStehle]

You also have to update the package version in the Directory.Build file

[chris-at-tyler]

Updated. I bumped the shared package version in Directory.Build.props to 8.0.1 and pushed the change to this PR branch.