Update Release Doc

[kim-tsao]

What does this PR do?:

• Update the Release doc to clarify our approach to versioning and support.
• Document the approach to separate the API releases from the Devfile release

Which issue(s) this PR fixes:

#585

PR acceptance criteria:

Testing and documentation do not need to be complete in order for this PR to be approved. We just need to ensure tracking issues are opened.

• Open new test/doc issues under the devfile/api repo
• Check each criteria if:
• There is a separate tracking issue. Add the issue link under the criteria
  or
• test/doc updates are made as part of this PR
• If unchecked, explain why it's not needed

• Unit/Functional tests

• QE Integration test

• [ X] Documentation

doc changes only

• Client Impact

How to test changes / Special notes to the reviewer:

[elsony]

/lgtm

[johnmcollier]

Nice changes 👍

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: amisevsk, elsony, johnmcollier, kim-tsao

The full list of commands accepted by this bot can be found here.

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• OWNERS

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[openshift-ci]

New changes are detected. LGTM label has been removed.