Introduce templates for specific issue types (#8842)

This replaces the single github issue-reporting template with templates for the
following types of issues:

* Build issues
* Spack command errors
* Feature request

Each template includes suggestions which are generally useful for the type of
issue encountered.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,49 @@
+---
+name: Bug report 
+about: Report a bug in the core of Spack (command not working as expected, etc.) 
+
+---
+
+
+*Explain, in a clear and concise way, the command you ran and the result you were trying to achieve.
+Example: "I ran Spack find to list all the installed packages and..."*
+
+
+
+### Steps to reproduce the issue
+
+```console
+$ spack <command1> <spec>
+$ spack <command2> <spec>
+...
+```
+
+### Error Message
+
+If Spack reported an error, provide the error message. If it did not report an error
+but the output appears incorrect, provide the incorrect output. If there was no error
+message and no output but the result is incorrect, describe how it does not match
+what you expect. To provide more information you might re-run the commands with 
+the additional -sd flags:
+```console
+$ spack -sd <command1> <spec>
+$ spack -sd <command2> <spec>
+...
+```
+that activate the full debug output. 
+
+
+### Information on your system
+
+This includes:
+
+ 1. which platform you are using
+ 2. any relevant configuration detail (custom `packages.yaml` or `modules.yaml`, etc.)
+
+-----
+
+We encourage you to try, as much as possible, to reduce your problem to the minimal example that still reproduces the issue. That would help us a lot in fixing it quickly and effectively!
+
+If you want to ask a question about the tool (how to use it, what it can currently do, etc.), try the `#general` channel on our Slack first. We have a welcoming community and chances are you'll get your reply faster and without opening an issue.
+
+Other than that, thanks for taking the time to contribute to Spack!