Add support-policy external reference type

[ppkarwasz]

Adds a new external reference type to reference documents such as:

• a Common Lifecycle Enumeration document.
• an OpenEOX document.
• a human-readable document specifying end-of-life or end-of-support dates for the CycloneDX component.

Closes #591

[jkowalleck]

a Common Lifecycle Enumeration document.

this is much too early. TC54-TG3 did not publish anything yet - so there is no standard/spec to use, or is there?

an OpenEOX document.

I tried very hard to find any standard/spec, but I failed. It appears that OpenEOX is still work-in-progress, as the only thing they've published is a structural proposal - and they are still working on the taxonomy, right?

a human-readable document [...]

I don't see much value in this. Well, it's something, but nothing i would consider valuable in any scale.

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this being said, I will put this PR in "DRAFT" mode.
If you think this was a mistake, please let us know.

[ppkarwasz]

this is much too early. TC54-TG3 did not publish anything yet - so there is no standard/spec to use, or is there?

There is a draft in Ecma-TC54/tg3#3

a human-readable document [...]

I don't see much value in this. Well, it's something, but nothing i would consider valuable in any scale.

While a human-readable document is a poor replacement for a machine-readable one, there is some value in having a direct link to an HTML page that lists all officially supported versions.

Many projects (including some of mine) don't even have such an HTML page, so determining if a version is supported requires a lot of Googling and guesswork.

this being said, I will put this PR in "DRAFT" mode.
If you think this was a mistake, please let us know.

That's fine by me.