Remove unnecessary public APIs for creating KeyValue structs

[utpilla]

We have an additional set of public APIs to create KeyValue struct apart from KeyValue::new(). These APIs don't offer anything additional in terms of feature or performance. They simply offer an alternative way to create KeyValue struct by creating the Key first and then the Value instead of having them created together.

I think we could remove these APIs just to keep our public API surface smaller. I'm opening this issue to check if anyone has any opinions on this.

opentelemetry-rust/opentelemetry/src/common.rs

Lines 36 to 73 in 66f29b8

	pub fn bool<T: Into<bool>>(self, value: T) -> KeyValue {
	KeyValue {
	key: self,
	value: Value::Bool(value.into()),
	}
	}
	/// Create a `KeyValue` pair for `i64` values.
	pub fn i64(self, value: i64) -> KeyValue {
	KeyValue {
	key: self,
	value: Value::I64(value),
	}
	}
	/// Create a `KeyValue` pair for `f64` values.
	pub fn f64(self, value: f64) -> KeyValue {
	KeyValue {
	key: self,
	value: Value::F64(value),
	}
	}
	/// Create a `KeyValue` pair for string-like values.
	pub fn string(self, value: impl Into<StringValue>) -> KeyValue {
	KeyValue {
	key: self,
	value: Value::String(value.into()),
	}
	}
	/// Create a `KeyValue` pair for arrays.
	pub fn array<T: Into<Array>>(self, value: T) -> KeyValue {
	KeyValue {
	key: self,
	value: Value::Array(value.into()),
	}
	}

[cijothomas]

@TommyCpp Do you know if there is a strong reason why this should be kept?

[TommyCpp]

This is mostly for ergonomics. We can remove it if we want to control API surface.

If user really wants it they can

pub trait CreateKeyValue {
   fn f64(value: f64) -> KeyValue
}

impl CreateKeyValue for Key {
      pub fn f64(self, value: f64) -> KeyValue {
        KeyValue::new(self, value)
    }
} 


// in other files
use CreateKeyValue;

let _ = Key::new("test").f64(1.0)

[utpilla]

Completed in #2091