Unable to upgrade in unprivileged mode on Windows

[blakerouse]

I created PR #4642 that adds upgrade testing for Windows when installed in unprivileged mode. It seems to have identified an issue where the elastic-agent-user is unable to create the symlink upon upgrade.

    fixture.go:656: >> running binary with: [C:\Users\windows\AppData\Local\Temp\TestStandaloneUpgradeWithGPGFallback2716514207\001\elastic-agent-8.14.0-SNAPSHOT-windows-x86_64\elastic-agent.exe install --force --non-interactive --unprivileged]
    fixture.go:656: >> running binary with: [C:\Program Files\Elastic\Agent\elastic-agent.exe status --output json]
    upgrader.go:295: Upgrading from version "8.14.0-SNAPSHOT-8bfc26c3063c53a7dae338af731e055e2819a456" to version "8.14.0-SNAPSHOT-372976eba8bcdf22e5a3a96c057f39b69bee1a13"
    fixture.go:656: >> running binary with: [C:\Program Files\Elastic\Agent\elastic-agent.exe upgrade 8.14.0-SNAPSHOT --pgp abcDEFgGIN PGP PUBLIC KEY BLOCK-----
        Version: GnuPG v2.0.14 (GNU/Linux)
        
        mQENBFI3HsoBCADXDtbNJnxbPqB1vDNtCsqhe49vFYsZN9IOZsZXgp7aHjh6CJBD
        A+bGFOwyhbd7at35jQjWAw1O3cfYsKAmFy+Ar3LHCMkV3oZspJACTIgCrwnkic/9
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        KiFv9jQrg2TIWEvzYx9tywTCxc+FFMWAlbCzi+m4WD+QUWWfDQ009U/WM0ks0Kww
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        qPDlGRlOgVTd9xUfHFkzB52c70E=
        =92oX
        -----END PGP PUBLIC KEY BLOCK-----
        ]
    upgrade_gpg_test.go:91: 
        	Error Trace:	C:/Users/windows/agent/testing/integration/upgrade_gpg_test.go:91
        	Error:      	Received unexpected error:
        	            	failed to start agent upgrade to version "8.14.0": exit status 1
        	            	Error: Failed trigger upgrade of daemon: failed to update agent symlink: symlink C:\Program Files\Elastic\Agent\data\elastic-agent-8.14.0-SNAPSHOT-372976\elastic-agent.exe C:\Program Files\Elastic\Agent\elastic-agent.exe.prev: A required privilege is not held by the client.
        	            	rolling back install: restoring symlink to "C:\\Program Files\\Elastic\\Agent\\data\\elastic-agent-8.14.0-SNAPSHOT-8bfc26\\elastic-agent" failed: failed to update agent symlink: symlink C:\Program Files\Elastic\Agent\data\elastic-agent-8.14.0-SNAPSHOT-8bfc26\elastic-agent.exe C:\Program Files\Elastic\Agent\elastic-agent.exe.prev: A required privilege is not held by the client.
        	            	For help, please see our troubleshooting guide at https://www.elastic.co/guide/en/fleet/8.14/fleet-troubleshooting.html
        	Test:       	TestStandaloneUpgradeWithGPGFallback

For confirmed bugs, please report:

• Version: 8.14
• Operating System: Windows

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)