Add CODEOWNERS and issue/pr templates (#203)

Author: chingor13

.github/CODEOWNERS

@@ -0,0 +1 @@
+* @googleapis/yoshi-java

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,36 @@
+Thanks for stopping by to let us know something could be better!
+
+Please include as much information as possible:
+
+#### Environment details
+
+- OS:
+- Java version:
+- google-auth-library-java version(s):
+
+#### Steps to reproduce
+
+1. ?
+2. ?
+
+#### Stacktrace
+
+```
+Any relevant stacktrace here.
+```
+
+#### Code snippet
+
+```java
+Any relevant code snippet to help reproduce the issue.
+```
+
+#### External references such as API reference guides used
+
+- ?
+
+#### Any additional information below
+
+Following these steps will guarantee the quickest resolution possible.
+
+Thanks!

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1 @@
+Fixes #<issue_number_goes_here> (it's a good idea to open an issue first for context and/or discussion)