Extract "Code Strategy Assessment Framework" into its own pattern

The Unified Source Code Inventory mentions the concept of a Source Code Strategy Assessment Framework.

I believe that such a framework could be useful even for companies that are only using a single version control system, and hence don't need to unify their source code inventory further (because they already have a single inventory).

Therefore I am proposing to pull the Source Code Strategy Assessment Framework into a pattern of its own, which can then be references from the Unified Source Code Inventory and other patterns.

从 patterns/1-initial/source-code-inventory.md 开始，审阅 trieshard/source-strategy-assessment 中链接的 Source Code Strategy Assessment Framework。将 framework 定义为一个独立的 pattern，然后更新 Unified Source Code Inventory 和其他相关 pattern，使其引用该 framework。完成的标准是：该 framework 已被独立记录，且现有引用都指向它。