SIEM "Additional look-back time" UI logic clobbers partial hours: e.g. 73 minutes becomes 1h in the UI

[bczifra]

Kibana version: 7.8.0

Elasticsearch version: 7.8.0

Describe the bug:
If a detection rule sets an "Additional look-back time" using minutes or seconds to what equates to a fractional hour, the rule is persisted correctly, and the API returns the response correctly. However, that UI clobbers response, taking the floor of the fractional hour. So, 67 minutes gets displayed as 1h, 139 minutes gets rendered as 2h. I think I've been able to track down the responsible UI code that clobbers it:

export const getHumanizedDuration = (from: string, interval: string): string => {
  const fromValue = dateMath.parse(from) ?? moment();
  const intervalValue = dateMath.parse(`now-${interval}`) ?? moment();

  const fromDuration = moment.duration(intervalValue.diff(fromValue));
  const fromHumanize = `${Math.floor(fromDuration.asHours())}h`;

  if (fromDuration.asSeconds() < 60) {
    return `${Math.floor(fromDuration.asSeconds())}s`;
  } else if (fromDuration.asMinutes() < 60) {
    return `${Math.floor(fromDuration.asMinutes())}m`;
  }

  return fromHumanize;
};

If I read this right, a duration as seconds of greater than or equal to 60 will be set to:

const fromHumanize = `${Math.floor(fromDuration.asHours())}h`;

which will round down to the nearest whole hour.

Steps to reproduce:

1. Create a new rule, or edit an existing rule, and set the "Additional look-back time" to 137 minutes
2. Save the rule
3. View the rule and you'll see 2h displayed.

Expected behavior: Either see the time in the original units entered, or as some fractional value of a larger order of magnitude unit.

[elasticmachine]

Pinging @elastic/siem (Team:SIEM)

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security Solution)

[MadameSheema]

Fixed on 7.10BC4