Refactor tedge_api::health module

[PradeepKiruvale]

Is your feature improvement request related to a problem? Please describe.

The tedge_api::health module must be refactored for better parsing of health status. And the same HealthStatus struct can be used across all the consumers to be in sync.

Describe the solution you'd like

Create the HealthStatus struct into the tedge_api::health module as follows:

#[derive(Debug, Serialize, Deserialize, PartialEq, Eq, Clone)]
pub struct HealthStatus {
    status: String,
    pid: u32,
    #[serde(with = "time::serde::rfc3339")]
    pub time: OffsetDateTime,
}

with on-the-fly transformation of the time field.

Then this same struct can be consistently used across all the consumer crates like converter, watchdog etc.

Make health_status_up_message() API accept an additional Option<OffsetDateTime> parameter so that the timestamp can be controlled from outside(mainly from tests).

Describe alternatives you've considered

Additional context