Only redact non-short secrets ending in suffix

[DrJosh9000]

What

• Only redact secrets that are at least 6 characters long
• Only redact secrets from env vars that strictly have one of the suffixes, not merely contained anywhere in the string

Why

Addresses buildkite/agent#3588

Unlike the standard environment-variable-based secret redaction in the agent, which implements the two rules above, buildkite-agent redactor add will add nearly any arbitrary string to the redactors for the current job. This behaviour allows users to more flexibly redact particular strings that don't necessarily conform to the default limits by calling buildkite-agent redactor add. Since we're calling it, we should apply the default rules.

[AliSoftware]

Damn, I only saw you opened this after I worked on it and opened my own PR #146 😅

I see that yours also introduces the MinSecretSize 👍 while mine doesn't. [EDIT] Actually I added the check on size as well now

That being said, mine adds unit tests too, so maybe still worth a look?