Fix sentinel-dashboard.log wrong path problems

[furaul]

Describe what this PR does / why we need it

Fix sentinel-dashboard.log wrong path problems while user defined {csp.sentinel.log.dir}.

Does this pull request fix one issue?

https://github.com/alibaba/Sentinel/issues/3434

Describe how you did it

correct logging.file.name setting in sentinel-dashboard/src/main/resources/application.properties.

Describe how to verify it

1. add -Dcsp.sentinel.log.dir=/Users/XXXX/logs1 in VM options.
2. While the DashboardApplication startup, the ${user.home}/logs/csp will not be created.

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