Share HttpClient to OIDC metadata document retriever

[drub0y]

The HttpClient was not being shared with the ConfigurationManager<OpenIdConnectConfiguration>. Needed to pass the instance into the constructor overload so that it is used by the OpenIdConnectConfiguration when fetching the document.

Fixes #1595.

[coveralls]

Pull Request Test Coverage Report for Build 53306

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 76.121%

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Totals
Change from base Build 53133:	0.0%
Covered Lines:	4361
Relevant Lines:	5729

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💛 - Coveralls

[cleemullins]

No issues found in Microsoft.Bot.Builder.dll
No issues found in Microsoft.Bot.Builder.AI.Luis.dll
No issues found in Microsoft.Bot.Builder.AI.QnA.dll
No issues found in Microsoft.Bot.Builder.ApplicationInsights.dll
No issues found in Microsoft.Bot.Builder.Azure.dll
No issues found in Microsoft.Bot.Builder.Dialogs.dll
No issues found in Microsoft.Bot.Builder.TemplateManager.dll
No issues found in Microsoft.Bot.Configuration.dll
No issues found in Microsoft.Bot.Connector.dll
No issues found in Microsoft.Bot.Schema.dll

[cleemullins]

The rumor on the street (from Dana) is that even with this change the problem is still present. He's diving deeper into the issue now that he's got a proxy environment setup.

[dmvtech]

@cleemullins It was user (my) error. All looks good. No errors implimenting @drub0y's branch and I can see the requests going through the proxy when implemented.