Review featuregate States and removal version

[bogdandrutu]

There are some caveats that I found while working with this API/functionality:

• Removal date suppose to be the date when feature gate will be removed, but that is irrelevant since once it is marked as Stable cannot be changed anyway. See https://github.com/open-telemetry/opentelemetry-collector/blob/main/featuregate/registry.go#L150 #7621
• I saw a need of having a "deprecated" State since sometimes a feature may fail and we want to mark the end of life for a gate that is not "stable" (successful). This state should be equivalent in capabilities (not allowing to be set, etc.) with Stable, but force the gate to be "false" (unsuccessful).
• It will be good to have a "from" date as well to mark when a gate was added. This way at the beginning of each release (or right before) we can build a table like https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates-removed/#feature-gates-that-are-removed

[bogdandrutu]

Marked as resolve, extracted what is left in a separate issue.