Better log redaction controls

### Description of the feature request:

Currently, Bazel's [`SafeRequestLogging`](https://cs.opensource.google/bazel/bazel/+/82e3f853f64892a5d7ad131186295117acd88087:src/main/java/com/google/devtools/build/lib/runtime/SafeRequestLogging.java) class has a [static set of strings to redact](https://cs.opensource.google/bazel/bazel/+/82e3f853f64892a5d7ad131186295117acd88087:src/main/java/com/google/devtools/build/lib/runtime/SafeRequestLogging.java;drc=82e3f853f64892a5d7ad131186295117acd88087;l=29) from the environment in the log:

```
private static final Pattern suppressFromLog =
Pattern.compile(
"--client_env=([^=]*(?:auth|pass|cookie|token|api_key)[^=]*)=", Pattern.CASE_INSENSITIVE);
```

It would be very useful to have an additional way to extend this list for other secrets.

Ideally this would be an environment variable, or a Java system property to make it easier to set globally. A bazel flag would also be acceptable (it could be used with a global bazelrc), but this is a little more work to set up.

### Which category does this issue belong to?

Core

### What underlying problem are you trying to solve with this feature?

User secrets appearing in logs.