* Lowercase OpenAPI document name on registration to match AddOpenApi internal behaviour
AddOpenApi lowercases the document name when registering its keyed services, so
ReplaceOpenApiSchemaService must receive the same lowercased key or the lookup
throws. BackOfficeOpenApiDocumentBuilder now computes a normalised registration
name and uses it for all DI calls, while keeping DocumentName in its original
casing. ShouldInclude matches [MapToApi] case-insensitively to align with how
documents are registered, and the UI dropdown label falls back to DocumentName
(original casing) rather than the lowercased registration key.
AddUmbracoOpenApiDocument applies the same normalisation for its apiName parameter.
* Add regression tests for mixed-case OpenAPI document name registration
Covers the bug scenario where AddBackOfficeOpenApiDocument with a mixed-case
name and WithJsonOptions threw InvalidOperationException at startup, and verifies
that ShouldInclude matches [MapToApi] case-insensitively.
