.gitattributes: Prevent line ending conversion

Unsets the text attribute on all files to prevent their line endings
from being normalized.

See https://git-scm.com/docs/gitattributes for background.

This was previously accomplished solely by instructing users to set
core.autocrlf to false. However, that is usually not possible in CI
environments such as pipelines and GitHub Actions where agents are
running on different operating systems. Changing the git configuration
in those environments requires the system level git configuration to
be modified prior to checkout since git configs cannot be checked into
a repo and automatically used for security reasons.

This is a simple way to check the change into the repo so it applies
for all users to prevent line ending conversion.

This allows CI plugins and scripts to produce similar line ending
results on Linux and Windows agents.

Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>

.gitattributes

@@ -0,0 +1 @@
+* -text