Add breaking change mitigations section and checklist item

Author: ycombinator

.github/PULL_REQUEST_TEMPLATE.md

@@ -35,6 +35,15 @@ List here all the items you have verified BEFORE sending this PR. Please DO NOT
 - [ ] I have added tests that prove my fix is effective or that my feature works
 - [ ] I have added an entry in `./changelog/fragments` using the [changelog tool](https://github.com/elastic/elastic-agent#changelog)
 - [ ] I have added an integration test or an E2E test
+- [ ] If this PR introduces a breaking change, I've populated the Breaking Change Mitigations section below.
+
+## Breaking Change Mitigations
+
+<!--
+If this PR introduces a breaking change for end users, describe what changes they could make on
+their end to nullify or minimize the impacts of this change. Consider impacts in related systems, not
+just directly when using Elastic Agent.
+-->
 
 ## Author's Checklist
 
@@ -59,7 +68,7 @@ Link related issues below. Insert the issue link or reference after the word "Cl
 - Requires #123
 - Superseds #123
 -->
-- 
+-
 
 ## Use cases
 
@@ -83,8 +92,8 @@ Paste here output logs discovered while creating this PR, such as stack traces o
 
 ## Questions to ask yourself
 
-- How are we going to support this in production? 
-- How are we going to measure its adoption? 
+- How are we going to support this in production?
+- How are we going to measure its adoption?
 - How are we going to debug this?
 - What are the metrics I should take care of?
 - ...