feat: add GitHub issue templates with default assignees

[tk-woven]

Description

This introduces issue templates for GitHub issues. Issue templates present issue creators with options between different pre-populated issue bodies. See FAIR's Detectron2 New-Issues for an example.

This also adds a number of default assignees. The default assignees are not required to solve the issues themselves, but they are added so that at least someone gets a notification when a new issue is opened. This way we can triage or re-assign as needed.

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This change is 

[tk-woven]

Added Wadim after discussing with him in-person.

Reviewable status: 0 of 3 files reviewed, all discussions resolved (waiting on @chrisochoatri, @kuanleetri, @ryo-takahashi-1206, @wadimkehl, and @ykkawana-woven)

[ryo-takahashi-1206]

Thank you for the PR 🙇
I confirmed the default assignees are set according to our last dicusssion.
Of course, no objection

Reviewed 3 of 3 files at r1.
Reviewable status: 1 of 3 files reviewed, all discussions resolved (waiting on @chrisochoatri, @kuanleetri, @ryo-takahashi-1206, @wadimkehl, and @ykkawana-woven)

[ryo-takahashi-1206]

Reviewable status: 1 of 3 files reviewed, all discussions resolved (waiting on @chrisochoatri, @kuanleetri, @ryo-takahashi-1206, @wadimkehl, and @ykkawana-woven)

[tk-woven]

Thanks, Ryo-san!

Reviewable status: 1 of 3 files reviewed, all discussions resolved (waiting on @chrisochoatri, @kuanleetri, @ryo-takahashi-1206, @wadimkehl, and @ykkawana-woven)

[wadimkehl]

NICE!

Reviewed 2 of 2 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @chrisochoatri, @kuanleetri, and @ykkawana-woven)

[tk-woven]

Thanks! I'll merge, and we can make adjustments based on others' feedback later if need be.

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @chrisochoatri, @kuanleetri, and @ykkawana-woven)