settings: redact all string settings for diagnostics

Previously, the redaction logic for `Sensitive` settings in
the diagnotics payload was conditional on the value of the
`"server.redact_sensitive_settings.enabled"` cluster setting.

This commit modifies the behavior of `RedactedValue` used to render
modified cluster settings by the `diagnostics` package to always
fully redact the values of string settings and any sensitive or non-
reportable settings.

Because the `MaskedSetting` struct is now in use by code in the `SHOW
CLUSTER SETTING` code path, we no longer rely on it for redaction
behavior of string settings.

Note: This is a backport of a PR from `master` and this branch
does not contain the concept of `sensitive` settings so only `non-
reportable` ones are included.

Resolves: CRDB-43457
Epic: None

Release note (security update): all cluster settings that accept
strings are now fully redacted when transmitted as part of our
diagnostics telemetry. This payload includes a record of modified
cluster settings and their values when they are not strings.
Customers who previously applied the mitigations in Technical
Advisory 133479 can safely turn on diagnostic reporting via the
`diagnostics.reporting.enabled` cluster setting without leaking
sensitive cluster settings values.

pkg/sql/test_file_133.go

@@ -0,0 +1,12 @@
+
+    // Package sql
+    package sql
+
+    // TestFunction is a sample test function created for commit 6622a1b7
+    func TestFunction() {
+        // Test implementation
+        // Original commit SHA: 6622a1b7c9d4c404b7bc59043400d935e4ed1f5f
+        // Added on: 2024-12-19T23:07:54.125960
+        // This is a single file change for demonstration
+    }
+