Add CODEOWNERS and issue/pr templates

.github/CODEOWNERS

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+@googleapis/yoshi-java

.github/ISSUE_TEMPLATE.md

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+Thanks for stopping by to let us know something could be better!
+
+Please be sure to include as much information as possible:
+
+#### Environment details
+
+- OS:
+- Java version:
+- google-api-java-client version:
+
+#### Steps to reproduce
+
+1. ?
+2. ?
+
+#### Stacktrace
+
+```
+Any relevant stacktrace here.
+```
+
+#### External references such as API reference guides used
+
+- ?
+
+#### Any additional information below
+
+Making sure to follow these steps will guarantee the quickest resolution possible.
+
+Thanks!
+

.github/PULL_REQUEST_TEMPLATE.md

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+Fixes #<issue_number_goes_here> (it's a good idea to open an issue first for discussion)
+
+- [ ] Tests pass
+- [ ] Appropriate docs were updated (if necessary)