Docs: Add note to contributing docs warning against tool based refactoring (#26936)

This commit adds a warning to deter contributers from creating PRs
generated by tools to do large refactors just for the sake of
refactoring.

Author: rjernst

CONTRIBUTING.md

@@ -38,6 +38,11 @@ If you have a bugfix or new feature that you would like to contribute to Elastic
 
 We enjoy working with contributors to get their code accepted. There are many approaches to fixing a problem and it is important to find the best approach before writing too much code.
 
+Note that it is unlikely the project will merge refactors for the sake of refactoring. These
+types of pull requests have a high cost to maintainers in reviewing and testing with little
+to no tangible benefit. This especially includes changes generated by tools. For example,
+converting all generic interface instances to use the diamond operator. 
+
 The process for contributing to any of the [Elastic repositories](https://github.com/elastic/) is similar. Details for individual projects can be found below.
 
 ### Fork and clone the repository