Implement AWS AppConfig client service for Boolean typed feature flag

[lavenderses]

What

Support boolean feature in OpenFeature reuirements with AWS AppConfig

relates #1

How

As described in #1, AWS AppConfig configuration response schema is like following.

{
  "{key name}": {
    // "Add new flag" > "Create flag" > "Off" or "On"
    "enabled": boolean,
    // "Add new flag" > "Create flag" > "Attribute (optional)"
    "{other attribute key 1}": number | string | boolean | regex,
    ...
  }
}

If I try to support other feature flag type such as number, string, using Attribute is required.
So, I decied following specification.

Provider spec

If Application Author created feature flag with name feature-1 in AWS console, he have to add Attribute (this is optional in AWS AppConfig spec, but this provider implementation forces Application Author to configure it) with name flag_value as Application Author's desired type.

(see about attribute in AWS doc.)

For example, if Application Author wants to use feature flag named user_id_for_test as number 123, configuration in AWS console will be following.
Any other attribute except for flag_value will be ignored in this provider implementation.

feature flag name	user_id_for_test
attribute	flag_value
attribute type	number
attribute value	123

And, this provider implementation expects above and response will be like....

{
  "user_id_for_test": {
    "enabled": boolean,
    "flag_value": `Application Author's desired type`
  }
}

Provider feature flag evaluation behevior

1. Returns feature flag value from AWS config only following items is satisfied.
   a. feature flag is enabled in AWS console. (= AWS AppConfig toggle is "On")
   b. flag_value is exist in attribute.
   c. flag_value type is same as Application Author's expected type.
2. Returns reason = ERROR and errorCode = FLAG NOT FOUD when flag not found in AWS AppConfig.
3. Returns reason = DISABLED when this feature flag is not enabled in AWS console. (= AWS AppConfig toggle is "Off")
4. Returns reason = ERROR and errorCode = PARSE_ERROR when (1-a) does not satisfied
5. Returns reason = ERROR and errorCode = TYPE_MISMATCH when (1-b) does not satisfied

These logic is implemented in AwsAppConfigParser and AppConfigValueConverter.

See also OpenFeature specification doc.
https://openfeature.dev/specification/types

Notes

N/A

[lavenderses]

LGTM