Add support for search invoke

[Eric Dahlvang (EricDahlvang)]

Fixes #5643

OnInvokeActivityAsync here:
https://github.com/OfficeDev/Microsoft-Teams-Samples/blob/main/samples/bot-type-ahead-search-adaptive-cards/csharp/TypeaheadSearch/Bots/ActivityBot.cs#L85

Would be changed to:

protected override async Task<SearchInvokeResponse> OnSearchInvokeAsync(ITurnContext<IInvokeActivity> turnContext, SearchInvokeValue invokeValue, CancellationToken cancellationToken)
{
    var packageResult = JObject.Parse(await(new HttpClient()).GetStringAsync($"https://azuresearch-usnc.nuget.org/query?q=id:{invokeValue.QueryText}&prerelease=true"));
    if (packageResult == null)
    {
        // no results available, return 204
        return new SearchInvokeResponse
        {
            Type = "application/vnd.microsoft.search.searchResponse",
            StatusCode = 204
        };
    }
    else
    {
        var packageList = packageResult["data"]
            .Skip(invokeValue.QueryOptions.Skip)
            .Take(invokeValue.QueryOptions.Top)
            .Select(item => (item["id"].ToString(), item["description"].ToString()))
            .Select(item => new { title = item.Item1, value = item.Item1 + " - " + item.Item2 })
            .ToList();
        
        return new SearchInvokeResponse
        {
            Type = "application/vnd.microsoft.search.searchResponse",
            Value = JObject.FromObject(new { results = packageList }),
            StatusCode = 200
        };
    }
}

[Coveralls (coveralls)]

Pull Request Test Coverage Report for Build 296646

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 41 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 78.637%

---

Files with Coverage Reduction	New Missed Lines	%
/libraries/Microsoft.Bot.Builder/ActivityHandler.cs	41	67.79%

Totals
Change from base Build 296444:	-0.01%
Covered Lines:	25266
Relevant Lines:	32130

---

💛 - Coveralls

[johnataylor]

The validate logic looks pretty watertight to me. Maybe an extra unit test to prevent someone accidentally regressing this in the future.

[johnataylor]

nit: isn't nameof going to give you the C# identifier whereas what you really want in the error message is the JSON property name. OK this is perhaps a nit because the only difference in this case at the current time is the casing.

I'm assuming the json property attribute doesn't override the nameof result (can you even do that?)