[Pre-RFC] Switch to time based releases

Speaking as a company deploying TVM to production (look for our talk at the upcoming TVM conference!), it would help our release process if TVM had a more predictable release schedule/process.

Right now, it appears TVM is pursuing feature based releases, but this leads to release schedule and there are examples of many successful OSS projects switching to time based schedules (eg: Linux kernel, Ubuntu, Kafka, Rust) and here’s a writeup of some of the benefits and tradeoffs.

I wanted to open up a pre-RFC to get some thoughts and discussion first.