Doc update to introduce Tiered Platform Support Model

[rrschulze]

Description: This PR adds documentation to introduce a tiered platform support model for the OpenTelemetry Collector. The tiered platform support model provides clarity to the project and its users about how existing platforms are supported today and how requests for new platforms can be supported in future, while balancing between the aim to support as many platforms as possible and to guarantee stability for the most important platforms.

Link to tracking Issue: #8209

[linux-foundation-easycla]

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[mx-psi]

Thanks for writing this up! I did a first review; will be out for a couple weeks and take this back when I return :)

[aunshc]

Suggested change

The proposed additional platforms Linux on s390x (#378) and AIX on ppc64 ([#19195](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/19195#issuecomment-1458560971)) will be included into Tier 3 once they're added to the OpenTelemetry Collector as platforms.

The proposed additional platforms Linux on s390x ([#378](https://github.com/open-telemetry/opentelemetry-collector-releases/issues/378#issuecomment-1662371014)) and AIX on ppc64 ([#19195](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/19195#issuecomment-1458560971)) will be included into Tier 3 once they're added to the OpenTelemetry Collector as platforms.

[rrschulze]

Instead of linking to specific issue comments here, it is sufficient to link to the related issues. I will update the link for AIX on ppc64.

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[codecov]

Codecov Report

Patch has no changes to coverable lines.

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[mx-psi]

Looks good to me, just one suggestion about formatting. Thanks for your hard work on this @rrschulze!!

[codeboten]

Thanks for the writeup! Only a few comments.

[yurishkuro]

Q: what happens when a tier-3 platform build starts failing? Is the release process already resilient enough to such failures to ensure that the other platforms are still released?

[mx-psi]

Q: what happens when a tier-3 platform build starts failing? Is the release process already resilient enough to such failures to ensure that the other platforms are still released?

@yurishkuro Right now it would make the build fail, but it would be easy enough to temporarily exclude a particular platform from the build with a small PR that we can later revert. Maybe we can make it easier, if you have concrete ideas please file an issue :)

In any case IMO this text should be read as a guide to make decisions (what to do when we have a question such as "should we delay the release because of a problem specific to platform X?") than as a prescription on what our release pipeline should look like.