ServiceClientCredentials support for SkillHttpClient

[alopix]

Is your feature request related to a problem? Please describe.
In the old Skill SDK (botbuilder-skills), the SkillDialog supported passing in a IServiceClientCredentials object, which would be used in the old SkillHttpTransport to allow for adding different kinds of authentication or any type of request transformations when connecting to the skills.
With SkillHttpClient (mostly BotFrameworkHttpClient) only supports appId and appPassword authentication and nothing else anymore.

Describe the solution you'd like
It would be nice to be able to define some kind of middleware (or if you moved from axios to the azure ms-rest-js again) in order to transform the outgoing request.

Describe alternatives you've considered
There's no alternative as appId and appPassword are not secure enough for us, so we're using api keys in addition.

Additional context

[enhancement]

[tonyanziano]

@clearab Can you please comment on this? Thanks!

[clearab]

Thanks for bringing this to our attention - we'll triage and consider for inclusion in the next release.