fix(composer): Exclude test files from Composer production downloads

[klausi]

Test code should not end up in a production deployment for security reasons. Please exclude test code from Composer downloads. This can be done with https://blog.madewithlove.be/post/gitattributes/

Not sure if you also want to exclude other stuff like README and example files?

[pitbulk]

Maybe makes sense to allow on composer production only:

• docs
• lib/Saml2
• extlib
• certs
• settings_example.php
• advanced_settings_example.php
• CHANGELOG
• LICENSE
• README.md

and ignore the rest

[klausi]

I think with .gitattributes you have to specify a black list (stuff that you want to ignore). Composer is primitive when it looks at those lines, so I think a white list is not possible https://github.com/composer/composer/blob/master/src/Composer/Package/Archiver/GitExcludeFilter.php

[klausi]

What about the endpoint folder? I left that in. Same for the other *.php files in the root folder, people might want to use them for whatever reasons.

Otherwise I removed the demo* folders.

[pitbulk]

we may exclude endpoints as well and the rest of php files not listed in the previous list I shared ;)