fix: throttleHost is not array in ExternalRateLimit

[reaver-flomesh]

Description:

Testing done:

Affected area:

Functional Area
New Functionality	[ ]
CI System	[ ]
CLI Tool	[ ]
Certificate Management	[ ]
Control Plane	[ ]
Demo	[ ]
Documentation	[ ]
Egress	[ ]
Ingress	[ ]
Install	[ ]
Networking	[ ]
Observability	[ ]
Performance	[ ]
SMI Policy	[ ]
Security	[ ]
Sidecar Injection	[ ]
Tests	[ ]
Upgrade	[ ]
Other	[ ]

Please answer the following questions with yes/no.

1. Does this change contain code from or inspired by another project?

   • Did you notify the maintainers and provide attribution?

2. Is this a breaking change?

3. Has documentation corresponding to this change been updated in the fsm-docs repo (if applicable)?

[mergify]

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• title ~= ^(\[wip\]|\[backport\]|\[cherry-pick\])?( )?(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert)(?:\(.+\))?:

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• linear-history

[reaver-flomesh]

/lgtm