Make long-term-roadmap up to date

[gyliu513]

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In https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/roadmap.md#long-term-roadmap , there are some tasks In Progress, but no issue linking, it is difficult to find those task info. Can anyone update the doc a bit to reflect where can I get more info of those tasks via some document links? Thanks!

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What version did you use? Version: (e.g., v0.4.0, 1eb551b, etc)

What config did you use? Config: (e.g. the yaml config file)

Environment OS: (e.g., "Ubuntu 20.04") Compiler(if manually compiled): (e.g., "go 14.2")

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