[Feature Request] File based regex rules

### Product Area

The "code-analyzer" CLI

### Your Need or Problem

Allow for regex rules to be placed into their own files and referenced from `code-analyzer.yml` so that they can be more easily shared between projects instead of merging them into existing files.

### Your Desired Solution

Lets say we had the rule:
```yaml
name: Salesforce Code Analyzer Configuration
version: 1.0.0

rulesets: []

engines:
regex:
custom_rules:
ProhibitSuppressWarnings:
regex: /@SuppressWarnings\([^)]*\)|\/\/\s*NOPMD/gi
file_extensions: ['.apex', '.cls', '.trigger']
description:
'Prohibits the use of @SuppressWarnings annotations and
NOPMD comments in Apex code. Suppressions hide code quality
issues; prefer fixing the underlying problems or improving
rules instead.'
violation_message:
'Suppression of warnings is not allowed. Fix the underlying
issue or improve the rule instead of suppressing violations.'
severity: 'High'
tags: ['CodeStyle', 'Recommended']
```
I would like to take the details of that rule and put them in a different .yaml file, then refer to that .yaml file from code-analyzer.yml

### Alternatives Considered

Keep adding rules to code-analyzer.yml like today, using a pre-processor/script ahead of every run, etc

### Additional Context (Screenshots, Files, etc)

_No response_

### Workaround

_No response_

### Urgency

Low

code-analyzer.yml を読み込む CLI エントリポイントから開始し、regex custom_rules がどのようにパースされるかを追跡します。外部の YAML ルールファイルをどのように参照して共有できるかを確認し、そのうえで、代表的な CLI 実行において既存のインラインルールがファイルベースのルールと併用して引き続き動作することを検証します。

索引モデルが issue の本文から書いたものです。