Manually execute NuGet's .NET SDK integration tests for signing

[dtivel]

NuGet.Client's Dotnet.Integration.Test project contains the following signing-related tests. Where it makes sense, I'll rerun these tests manually by signing with Sign CLI and then verifying with NuGet in the .NET SDK.

Test	Result
DotnetSign_ResignPackageWithoutOverwrite_FailsAsync	✔️ Sign CLI always overwrites, so the expected results between NuGet and Sign CLI are different. That said, Sign CLI behaves as expected.
DotnetSign_ResignPackageWithOverwrite_SuccessAsync	✔️ same as above
DotnetSign_SignPackageWithExpiredCertificate_FailsAsync	➖ It's not possible to sign with an expired certificate in Sign CLI; Azure Key Vault automatically renews certificates.
DotnetSign_SignPackageWithInvalidEku_FailsAsync	✔️ Like NuGet, Sign CLI fails with an error like NU3018: NotValidForUsage: The certificate is not valid for the requested usage.
DotnetSign_SignPackageWithNotYetValidCertificate_FailsAsync	➖ It's not possible to sign with a not-yet-valid certificate in Sign CLI, because you cannot create one in Azure Key Vault.
DotnetSign_SignPackageWithOutputDirectory_SucceedsAsync	➖ Does not apply to Sign CLI.
DotnetSign_SignPackageWithOverwrite_SuccessAsync	✔️ Like NuGet, Sign CLI succeeds.
DotnetSign_SignPackageWithPfxFile_SuccessAsync	➖ Does not apply to Sign CLI.
DotnetSign_SignPackageWithPfxFileOfRelativePath_SuccessAsync	➖ Does not apply to Sign CLI.
DotnetSign_SignPackageWithPfxFileWithoutPasswordAndWithNonInteractive_FailsAsync	➖ Does not apply to Sign CLI.
DotnetSign_SignPackageWithRevokedLeafCertChain_FailsAsync	➖ Not feasible to test this with Sign CLI.
DotnetSign_SignPackageWithTimestamping_SucceedsAsync	✔️ Like NuGet, Sign CLI succeeds.
DotnetSign_SignPackageWithTrustedCertificate_SucceedsAsync	✔️ Like NuGet, Sign CLI succeeds.
DotnetSign_SignPackageWithTrustedCertificateWithRelativePath_SucceedsAsync	➖ Does not apply to Sign CLI.
DotnetSign_SignPackageWithUnknownRevocationCertChain_SucceedsAsync	➖ Not feasible to test this with Sign CLI.
DotnetSign_SignPackageWithUnsuportedTimestampHashAlgorithm_FailsAsync	❌ Found #624
DotnetSign_SignPackageWithUntrustedSelfIssuedCertificateInCertificateStore_SuccessAsync	➖ Not feasible to test this with Sign CLI.

CC @clairernovotny