internal/log: fix potential integer conversion issue from parsed value

[darccio]

What does this PR do?

Parses DD_LOGGING_RATE as int64 instead of uint64 to make sure, although it should contain a big value to happen, it doesn't yield unexpected results when converted to time.Duration.

Respects the current behaviour by taking into account that a zero value means to log immediately.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.

For Datadog employees:

• If this PR touches code that handles credentials of any kind, such as Datadog API keys, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2023-10-24 15:07:02

Comparing candidate commit 6a44811 in PR branch dario.castane/VULN-4830/fix-integer-types-conversion with baseline commit 5e9b0b1 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 40 metrics, 1 unstable metrics.