Add a link to code to find current set of transient errors

It will be good to document which errors the default strategy consider as transient.
In particular, I expected that Timeouts will be retried.
It is a reasonable expectation, e.g. In https://docs.microsoft.com/en-us/azure/azure-sql/database/troubleshoot-common-connectivity-issues?view=azuresql has
public bool IsTransient(Exception ex) //entLib 2013
if (ex is TimeoutException) { return true;

However it wasn’t correct - see https://github.com/dotnet/efcore/issues/27826.
Having explicit reference to list of transient errors will avoid the confusion.

The reference to transient errors list will be good also in https://docs.microsoft.com/en-au/ef/core/miscellaneous/connection-resiliency

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* ID: fcac28c8-acc4-81b6-01f6-6ffad57c64a1
* Version Independent ID: 9fcb9d42-63cf-af0a-14b0-ac470130b089
* Content: [SqlServerDbContextOptionsBuilder.EnableRetryOnFailure Method (Microsoft.EntityFrameworkCore.Infrastructure)](https://docs.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.infrastructure.sqlserverdbcontextoptionsbuilder.enableretryonfailure?view=efcore-6.0)
* Content Source: [dotnet/xml/Microsoft.EntityFrameworkCore.Infrastructure/SqlServerDbContextOptionsBuilder.xml](https://github.com/dotnet/EntityFramework.ApiDocs/blob/live/dotnet/xml/Microsoft.EntityFrameworkCore.Infrastructure/SqlServerDbContextOptionsBuilder.xml)
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