Improve logging pattern schema validation (#200317)

## Summary

This makes pattern schema validation stricter by avoiding unrestricted
matching, enforces realistic timezone constraints, and sets an upper
bound to the date format string.

| Characteristic | Before | After |
----|----|----|
| Optional Groups | Capturing groups for optional sections. |
Non-capturing groups for optional sections.|
|Timezone Validation | Allows any characters except }. | Restricts to
A-Za-z/_+-.|
|Clarity | More complex and verbose. | Cleaner, more restrictive, and
simpler.|
|Performance | Captures unnecessary groups. | Limits captures to needed
named groups.|

---------

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

packages/core/logging/core-logging-common-internal/src/layouts/conversions/date.ts

@@ -12,7 +12,7 @@ import { last } from 'lodash';
 import { LogRecord } from '@kbn/logging';
 import { Conversion } from './types';
 
-const dateRegExp = /%date({(?<format>[^}]+)})?({(?<timezone>[^}]+)})?/g;
+const dateRegExp = /%date(?:\{(?<format>[^}]+)\})?(?:\{(?<timezone>[A-Za-z/_+-]+)\})?/g;
 
 const formats = {
   ISO8601: 'ISO8601',
@@ -29,7 +29,6 @@ function formatDate(
 ): string {
   const momentDate = moment(date);
   momentDate.tz(timezone ?? moment.tz.guess());
-
   switch (dateFormat) {
     case formats.ISO8601:
       return momentDate.toISOString();

packages/core/logging/core-logging-server-internal/src/layouts/pattern_layout.test.ts

@@ -326,6 +326,21 @@ describe('schema', () => {
           `"Date format expected one of ISO8601, ISO8601_TZ, ABSOLUTE, UNIX, UNIX_MILLIS, but given: HH"`
         );
       });
+
+      it('fails on %date with schema too long', () => {
+        const generateLongFormat = () => {
+          const longFormat = [];
+          for (let i = 1; i < 1001; i++) {
+            longFormat.push(`${i}`);
+          }
+          return longFormat.join('');
+        };
+        expect(() =>
+          patternSchema.validate(`%date${generateLongFormat()}`)
+        ).toThrowErrorMatchingInlineSnapshot(
+          `"value has length [2898] but it must have a maximum length of [1000]."`
+        );
+      });
     });
   });
 });

packages/core/logging/core-logging-server-internal/src/layouts/pattern_layout.ts

@@ -24,6 +24,7 @@ import {
 const DEFAULT_PATTERN = `[%date][%level][%logger] %message`;
 
 export const patternSchema = schema.string({
+  maxLength: 1000,
   validate: (string) => {
     DateConversion.validate!(string);
   },