Use HashSet instead of string array for endorsement

[jineshjin]

Use this query to search for the most popular feature requests.

Is your feature request related to a problem? Please describe.
Yes as part of complexity

Describe the solution you'd like
we would like to have O(1) complexity instead of O(N)

Describe alternatives you've considered
Have to rely on O(N)

Additional context
As mentioned here: https://github.com/microsoft/botbuilder-js/blob/main/libraries/botframework-connector/src/auth/endorsementsValidator.ts#L50 when are we planning to use HashSet for endorsement.