Rewrite and formatting change to issue template

[ggunson]

This PR makes some changes to the issue template:

• fixed the markdown formatting of the checkbox list
• removed "for paid support and community users" on the first line because that's "everyone"?
• added the contents of the crashing bug page directly, because the ProxySQL docs on GitHub are deprecated, and there are duplicates listed there
  • added link to https://proxysql.com/contact-us/ for the "contact us" part of that; I'm not sure if that's what you want people to use?
• changed the "remember" line, as people are likely learning that this isn't the location for support questions as they're reading this
• added link to page about support contracts
• added default file location for the ProxySQL error log

Ideally the template would be set up where users could fill it in, rather than delete it in its entirety as I've been seeing, but I don't have any suggestions on how to do that.

[pondix]

Automated message: PR pending admin approval for build testing

[renecannao]

add to whitelist