[github]: add templates for submitting issues and PR (#947)

.github/ISSUE_TEMPLATE.md

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+<!--
+If you are reporting a new issue, make sure that we do not have any duplicates
+already open. You can ensure this by searching the issue list for this
+repository. If there is a duplicate, please close your issue and add a comment
+to the existing issue instead.
+
+If you suspect your issue is a bug, please edit your issue description to
+include the BUG REPORT INFORMATION shown below. If you fail to provide this
+information within 7 days, we cannot debug your issue and will close it. We
+will, however, reopen it if you later provide the information.
+
+For more information about reporting issues, see
+https://github.com/Azure/SONiC/wiki#report-issues
+
+---------------------------------------------------
+GENERAL SUPPORT INFORMATION
+---------------------------------------------------
+
+The GitHub issue tracker is for bug reports and feature requests.
+General support can be found at the following locations:
+
+- SONiC Support Forums - https://groups.google.com/forum/#!forum/sonicproject
+
+---------------------------------------------------
+BUG REPORT INFORMATION
+---------------------------------------------------
+Use the commands below to provide key information from your environment:
+You do NOT have to include this information if this is a FEATURE REQUEST
+-->
+
+**Description**
+
+<!--
+Briefly describe the problem you are having in a few paragraphs.
+-->
+
+**Steps to reproduce the issue:**
+1.
+2.
+3.
+
+**Describe the results you received:**
+
+
+**Describe the results you expected:**
+
+
+**Additional information you deem important (e.g. issue happens only occasionally):**
+
+    **Output of `show version`:**
+
+    ```
+    (paste your output here)
+    ```
+
+    **Attach debug file `sudo generate_dump`:**
+
+    ```
+    (paste your output here)
+    ```

.github/PULL_REQUEST_TEMPLATE.md

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+<!--
+Please make sure you've read and understood our contributing guidelines;
+https://github.com/Azure/SONiC/blob/gh-pages/CONTRIBUTING.md
+
+** Make sure all your commits include a signature generated with `git commit -s` **
+
+If this is a bug fix, make sure your description includes "fixes #xxxx", or
+"closes #xxxx"
+
+Please provide the following information:
+-->
+
+**- What I did**
+
+**- How I did it**
+
+**- How to verify it**
+
+**- Description for the changelog**
+<!--
+Write a short (one line) summary that describes the changes in this
+pull request for inclusion in the changelog:
+-->
+
+
+**- A picture of a cute animal (not mandatory but encouraged)**