Add .checkstyle to .gitignore

.checkstyle files should not be checked in.

Issue-ID: POLICY-2971
Change-Id: I0cd0a6558ea7e282a5dce4868fead1784362e555
Signed-off-by: liamfallon <liam.fallon@est.tech>
diff --git a/.gitignore b/.gitignore
index 67ad92d..a159c84 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,7 @@
 .project
 .buildpath
 .idea
+.checkstyle
 *.iml
 ui-react/node_modules
 ui-react/build