Update example config with UDP precision option

[gunnaraasen]

Required for all non-trivial PRs

• Sign CLA (if not already signed)
• Config changes: update sample config (etc/config.sample.toml), server NewDemoConfig method, and Diagnostics methods reporting config settings, if necessary

This updates the config and diagnostic info for the UDP service to include the precision option, which was added in PR #5565.

[rbetts]

Before we merge this documentation change, it looks like the original PR didn't include a testcase. Also, we need to review this for Enterprise in case this is a configuration stanza that needs to be updated in both places.

[mark-rushakoff]

Yep, looks like services/udp/service_test.go still hasn't been updated with a precision test case since that original PR. This PR so far looks good, but +1 to adding a test case.

[gunnaraasen]

Enterprise already has precision documented in the sample config file. I think not including it here was an oversight.

I've updated the text to reflect the Enterprise config snippet and also added precision to the UDP config test.

[rbetts]

Thanks for adding the test case.