Create a github issue template for proposing TSC meeting topics

To some extent, any issue opened on this repo could be considered a TSC meeting topic, but in today's meeting we discussed the notion of creating an issue template that let someone queue up a topic for a TSC meeting, indicating whether it could wait until the next regularly scheduled TSC meeting, or warrants holding a meeting to handle as soon as conveniently possible.

Start by checking how GitHub issue templates are configured in the TSC repository and whether other templates already exist. Define fields for the proposed topic and whether it can wait for the next regular TSC meeting or needs an earlier meeting; done when contributors can submit that information through a dedicated template.

Written by the indexing model from the issue text.