[github/templates] Add samples cmds to get OS env (#7550)

* [github/templates] Add samples cmds to get OS env When reporting bugs, users doesn't seem to know what information to report for the line "OS / Environment". - `uname -a`: Provide the arch + kernel (which has the dist tag name) - `grep -Hv ^# /etc/*release`: most of distribution provide some sort of /etc/*release file. Adding -H to get the filename too. And -v ^# to remove comments if any Example on my Fedora: ``` uname -a; grep -Hv ^# /etc/*release Linux munin 5.2.18-100.fc29.x86_64 #1 SMP Tue Oct 1 13:32:05 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux /etc/fedora-release:Fedora release 29 (Twenty Nine) /etc/os-release:NAME=Fedora /etc/os-release:VERSION="29 (Twenty Nine)" /etc/os-release:ID=fedora /etc/os-release:VERSION_ID=29 /etc/os-release:VERSION_CODENAME="" /etc/os-release:PLATFORM_ID="platform:f29" /etc/os-release:PRETTY_NAME="Fedora 29 (Twenty Nine)" /etc/os-release:ANSI_COLOR="0;34" /etc/os-release:LOGO=fedora-logo-icon /etc/os-release:CPE_NAME="cpe:/o:fedoraproject:fedora:29" /etc/os-release:HOME_URL="https://fedoraproject.org/" /etc/os-release:DOCUMENTATION_URL="https://docs.fedoraproject.org/en-US/fedora/f29/system-administrators-guide/" /etc/os-release:SUPPORT_URL="https://fedoraproject.org/wiki/Communicating_and_getting_help" /etc/os-release:BUG_REPORT_URL="https://bugzilla.redhat.com/" /etc/os-release:REDHAT_BUGZILLA_PRODUCT="Fedora" /etc/os-release:REDHAT_BUGZILLA_PRODUCT_VERSION=29 /etc/os-release:REDHAT_SUPPORT_PRODUCT="Fedora" /etc/os-release:REDHAT_SUPPORT_PRODUCT_VERSION=29 /etc/os-release:PRIVACY_POLICY_URL="https://fedoraproject.org/wiki/Legal:PrivacyPolicy" /etc/redhat-release:Fedora release 29 (Twenty Nine) /etc/system-release:Fedora release 29 (Twenty Nine) ``` * Update command to have MacOS and Unix working too