[api-extractor] Add config options to customize the "API signature changed" notice

[octogonz]

When API Extractor detects that the API report file has changed, it reports a notice to the end user.

If localBuild=false, you see this warning:

You have changed the public API signature for this project. 
Please overwrite ___ with a copy of ___ and then request an API review. 
See the Git repository README.md for more info.

If localBuild=true, you see this warning:

You have changed the public API signature for this project. Updating ___

We should provide a way to customize this message. Currently the only way to do that is to programmatically intercept API Extractor's logging, as seen in this workaround.

[octogonz]

PR #1211 makes a workaround fairly easy if API Extractor is invoked programmatically.

[boomler]

@octogonz How can i make it throws an error, when "API signature changed"?