Fix incorrect log paths.

[davinchia]

What

Log paths were missing a slash, causing certain cases on Cloud to drop logs. This PR fixes this.

How

Instead of concatenating strings, use the Path class to make sure slashes always exist.

Recommended reading order

1. LogClientSingleton.java

🚨 User Impact 🚨

Are there any breaking changes? What is the end result perceived by the user? If yes, please merge this PR with the 🚨🚨 emoji so changelog authors can further highlight this if needed.

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