security: Add notes for contrib dependencies with instructions

[ajgajg1134]

What does this PR do?

Clarify our policy for contrib dependency version upgrades and give users easy to follow instructions for upgrading

Motivation

We get a number of customers who are (rightfully) concerned about vulnerable versions their security tooling detects. This updated guide will hopefully help customers discover this information without having to open support requests and provides them clear guidance!

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: 2023-09-12 20:11:12

Comparing candidate commit 5049995 in PR branch andrew.glaude/security with baseline commit 246238d in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 39 metrics, 2 unstable metrics.