Ignore files when exporting package

This commit is part of a campaign to reduce the amount of data transferred to save global bandwidth and reduce the amount of CO2. See Codeception/Codeception#5527 for more info.

.gitattributes

@@ -0,0 +1,15 @@
+/.github export-ignore
+/tests export-ignore
+/upgrade export-ignore
+
+/.coveralls.yml export-ignore
+/.editorconfig export-ignore
+/.gitattributes export-ignore
+/.gitignore export-ignore
+/.travis.yml export-ignore
+/CHANGELOG.md export-ignore
+/changelog-linker.php export-ignore
+/ecs.php export-ignore
+/phpstan.neon export-ignore
+/phpunit.xml export-ignore
+/rector-ci.php export-ignore