feat: Add TryFromIterator trait and implement it for Labels and Annotations

[Techassi]

Fixes #713

It does not directly solve the issue, but .collect() only works on types which implement FromIterator which must never fail. Implementing FromIterator for Result<Self, Error> is also not an option, because we cannot implement a foreign trait on a foreign type. There are now two possible solutions.

Old

let map = BTreeMap::from([
    ("stackable.tech/managed-by", "stackablectl"),
    ("stackable.tech/vendor", "Stackable"),
]);

let labels = map
    .iter()
    .map(|p| Label::try_from(p))
    .collect::<Result<Vec<Label>, LabelError>>()
    .unwrap();

let labels = Labels::from_iter(labels);

New

let map = BTreeMap::from([
    ("stackable.tech/managed-by", "stackablectl"),
    ("stackable.tech/vendor", "Stackable"),
]);

// Works on any iterator, like Vec<(String, String)> or &[(&str, &str)]
let labels = Labels::try_from_iter(map).unwrap();

[NickLarsenNZ]

LGTM