Move extensions to Structured pattern (#512)

* Move extensions to Structured and add to mind map

Co-authored-by: Sukriti-Sharma4 <[email protected]>

Author: Ssukriti

book/en/toc.md

@@ -27,6 +27,7 @@ Instead edit toc_template.md
 * [Cross-Team Project Valuation](../../patterns/2-structured/crossteam-project-valuation.md) - It's hard to sell the value of cross-team InnerSource projects that don't provide a direct impact on company revenue. Here's a data-driven way to represent your project that both articulates its value and amplifies it.
 * [Dedicated Community Leader](../../patterns/2-structured/dedicated-community-leader.md) - Select people with both communications and technical skills to lead the communities to ensure success in starting an InnerSource initiative.
 * [Document your Guiding Principles](../../patterns/2-structured/document-your-guiding-principles.md) - The usual InnerSource explanation of "applying open source best practices inside an organisation" does not work well with people lacking an open source background. As a remedy the most important principles of InnerSource get documented and published widely.
+* [Extensions for Sustainable Growth](../../patterns/2-structured/extensions-for-sustainable-growth.md) - An InnerSource project is receiving too many contributions, making maintenance difficult. By offering an extension mechanism outside of the core project, the maintainers enable scaling of project capabilities with minimal cost and maintenance overhead.
 * [Gig Marketplace](../../patterns/2-structured/gig-marketplace.md) - Establish a marketplace by creating an intranet website that lists specific InnerSource project needs as "Gigs" with explicit time and skill requirements.  This will enable managers to better understand their employee’s time commitment and professional benefits thereby increasing the likelihood of garnering approval to make InnerSource contributions.
 * [InnerSource License](../../patterns/2-structured/innersource-license.md) - Two legal entities that belong to the same organization want to share software source code with each other but they are concerned about the implications in terms of legal liabilities or cross-company accounting.
 * [InnerSource Portal](../../patterns/2-structured/innersource-portal.md) - Potential contributors cannot easily discover InnerSource projects that they are interested in. By creating an intranet website that indexes all available InnerSource project information you enable contributors to learn about projects that might interest them and InnerSource project owners to attract an outside audience.

pattern-categorization/innersource-program-mind-map.md

@@ -121,3 +121,9 @@
 #### Lack of open source knowledge
 
 ##### [Document your Guiding Principles](https://patterns.innersourcecommons.org/p/document-your-guiding-principles)
+
+### Technical Challenges
+
+#### Increasing maintenance overhead
+
+##### [Extensions for Sustainable Growth](https://patterns.innersourcecommons.org/p/extensions-for-sustainable-growth)

patterns/1-initial/extensions-for-sustainable-growth.md renamed to patterns/2-structured/extensions-for-sustainable-growth.md

@@ -103,7 +103,7 @@ Extensions to Manage Contributions at Scale
 
 ## Status
 
-Initial
+Structured
 
 ## Author(s)