[enhancement] Add Functional Options for Configuring ExponentialBackOff

[KhanSufiyanMirza]

Description:
As part of enhancing the usability of the backoff library, I propose adding functional options for configuring the ExponentialBackOff struct. Functional options provide a more flexible and extensible way to set various parameters for the ExponentialBackOff.

Feature Details:

• Add functional options for InitialInterval, RandomizationFactor, Multiplier, MaxInterval, MaxElapsedTime, StopDuration, and Clock.
• Update NewExponentialBackOff to accept these functional options.

Expected Behavior:
Developers will be able to easily configure the ExponentialBackOff struct with the desired parameters using functional options. This will make the library more user-friendly and customizable.
backOff := NewExponentialBackOff( WithInitialInterval(1*time.Second), WithMultiplier(2.0), WithMaxInterval(10*time.Second), WithMaxElapsedTime(30*time.Second), WithRetryStopDuration(0), WithClockProvider(SystemClock), )

Motivation:
This feature will enhance the library by allowing users to configure the ExponentialBackOff struct in a more intuitive and extensible way. It aligns with best practices for creating flexible APIs.

Additional Information:

• I have prepared the code changes and unit tests.
• A pull request is submitted.

Please let me know your thoughts and whether this feature aligns with the project's goals.

[jcass8695]

@cenkalti could you create a tag for this please?

[rcontreras-te]

@cenkalti v4.2.1 doesn't have this in it... could we get a next release please? (cc: @KhanSufiyanMirza )

[cenkalti]

Tagged as v4.3.0