Add additional labels for host functions

[chevdor]

Suggestion from @koute from paritytech/polkadot#7158

Suggestion

• one label for when we introduce a new host function (host function is not used yet, so no need for everyone to upgrade; low priority)
• one label for when we enable a previously unused host function (everyone has to upgrade; high priority)
• one label for when we modify a previously unused but already existing in in-the-wild host function (so that if we enable it we know what is the oldest version of node that's still compatible)

cc @the-right-joyce

[chevdor]

This kind of granularity allows being super accurate when listing/grouping those PRs.

This will however only work if those extra labels are used properly by everyone and picking the right set of labels has an overhead. We have already lots of labels and I know the amount if already daunting. That being said, the number of people working around host functions is limited so it may work.

[the-right-joyce]

as we're currently re-working on labels and we will need a new release process for the monorepo, I'd say we don't start tinkering around now
But the idea is good and should be include in: paritytech/labels#25