src: add process.release.lts property & LTS CODENAME VOTING

Looking for review of this against v4.x, and separately calling for votes from @nodejs/collaborators on what the codename for our first LTS line (v4.x) will be. We are aiming for v4.2.0 LTS to be released this Thursday so this has to be quick!

Adopting a codename for LTS releases is part of the original LTS plan and although we've had a couple of late-breaking objections to even having a codename we're going ahead with it anyway given that this has been baked into the LTS plan that has already been adopted. We'll give it a go for this first one and assess for v6 if we go ahead and do it again.

The objectives are something like this:

• Something fun
• Something to set the LTS releases apart from the standard releases, both technically (a process.release.lts property) and for non-code communication purposes. We have an additional burden of having to start an LTS at an arbitrary point of a semver-major + semver-minor, i.e. 4.2.0 in this case, being able to call it something from that point on sets it apart
• Foster a shared culture around LTS as more than just another release line, having input on what the codename should be from the broader group also helps with a sense of shared ownership (also, fun again, imagine how boring Ubuntu would be without the fun names? It'd be as boring as Fedora has become)

The plan was for the @nodejs/lts group to come up with a short-list and call for voting. We've decided to go with the periodic-table for inspiration, there's a nice connection between the elements and the elemental nature of what we are trying to do with Node (i.e. small-core), also, there's lots to choose from! We also agreed that using alphabetic ordering will be helpful in deciphering order without needing additional context if people choose to refer to a line by its codename. These are what are available:

• Actinium Ac
• Aluminum Al
• Americium Am
• Antimony Sb
• Argon Ar
• Arsenic As
• Astatine At

For various reasons we've had to trim that list right down and only have two candidates for the v4 LTS codename:

Actinium

Actinium is a silvery radioactive metallic element. Actinium glows in the dark due to its intense radioactivity with a blue light. Actinium was discovered in 1899 by André-Louis Debierne, a French chemist, who separated it from pitchblende. Friedrich Otto Giesel independently discovered actinium in 1902. The chemical behavior of actinium is similar to that of the rare earth lanthanum. The word actinium comes from the Greek aktis, aktinos, meaning beam or ray. Also, Actinium happens to have 4 isotopes, which is nice for our v4 release.

Argon

Argon was suspected to be present in air by Henry Cavendish in 1785 but wasn't discovered until 1894 by Lord Rayleigh and Sir William Ramsay. Argon is the third noble gas, in period 8, and it makes up about 1% of the Earth's atmosphere. Argon has approximately the same solubility as oxygen and it is 2.5 times as soluble in water as nitrogen . This chemically inert element is colorless and odorless in both its liquid and gaseous forms. It is not found in any compounds. This gas is isolated through liquid air fractionation since the atmosphere contains only 0.94% argon. The Martian atmosphere in contrast contains 1.6% of Ar-40 and 5 ppm Ar-36. World production exceeds 750.000 tonnes per year, the supply is virtually inexhaustible.

(Astatine might also have been in the running except for the slightly awkward pronunciation and this gem: "total world production of astatine to date is estimated to be less than a millionth of a gram, and virtually all of this has now decayed away.")

So, this vote is open to @nodejs/collaborators only, you get one vote each, just leave a comment with your choice below.

Also looking for reviews of the changes this introduces (assuming the codename will be inserted to the appropriate places when chosen).