[COMMUNITY] remove mentions of JIRA, update community docs

[szha]

Description

remove mentions of JIRA, update community docs

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• Changes are complete (i.e. I finished coding on this PR)
• Code is well-documented

Changes

• remove mentions of JIRA
• update community docs (credit: many are adapted from tvm)
• update github template
• create RFC issue template

Comments

• https://lists.apache.org/thread.html/rc2b2615fd9b43d90f35b584621e1f57c08e221061ffdef60c15c14cb%40%3Cdev.mxnet.apache.org%3E

[mxnet-bot]

Hey @szha , Thanks for submitting the PR
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[ys2843]

Preview link: http://ec2-34-219-134-42.us-west-2.compute.amazonaws.com/

[ys2843]

Sorry I wasn't accurate about the clipboard trigger, wrapping code inside either ```bash or {% highlight bash %} works the same. But in the new contributes docs, ``` {.bash} was used which won't trigger the clipboard.
I suggest reverting the last commit, and only update the new docs to use either ```bash or {% highlight bash %}, and not touching the rest of tutorials and api markdowns as the clipboard works on those pages.

[szha]

OK

[szha]

@mxnet-bot run ci [unix-cpu, windows-gpu]

[mxnet-bot]

Jenkins CI successfully triggered : [windows-gpu, unix-cpu]