DevX API Reliability Issue

[peombwa]

Describe the bug
500 out-of-memory error when calling DevX API with forceRefresh=true when graphVersion is beta and intermittently in v1.0.

To Reproduce
Steps to reproduce the behavior:

1. Open https://graphexplorerapi.azurewebsites.net/openapi/operations?openapiversion=3&style=Powershell&graphVersion=beta&forceRefresh=true from your browser.
2. See error: {"StatusCode":500,"Message":"Exception of type 'System.OutOfMemoryException' was thrown."}

Expected behavior
An OpenAPI document should be returned when forceRefresh=true.

Additional context
The issue is blocking PowerShell's weekly OpenAPI refreshes from getting the latest API refreshes.

[irvinesunday]

According to App Insights telemetry, this is where the exception gets thrown:

microsoft-graph-devx-api/OpenAPIService/OpenApiService.cs

Line 665 in 7114d5f

var doc = new OpenApiStringReader().Read(sb.ToString(), out _);

.
During fixing of references in the OpenAPI document, the document is first serialized into a StringBuilder object. The conversion of the StringBuilder object to a string and the OpenAPI.NET library method that reads this string (OpenApiStringReader().Read()) ends up allocating a significant amount of memory for this process, especially for beta paths, which are appr. double the size of v1.0 paths. There is need to review this fixing of references.

[irvinesunday]

This has been temporarily resolved by scaling up the DevX API app service plan to allocate more memory.