When downloading JSON Schema files, do Conditional GETs

[madskristensen]

The requests coming in for JSON Schema files to SchemaStore.org don't check if the remote files have changed before downloading them. This puts unneeded pressure on the SchemaStore.org servers and it downloads more data than needed which will cost money for users that pay bandwidth by the megabyte.

By supporting Conditional GETs (HTTP 304) using either If-Modified-Since or If-None-Match request header, these issues are fixed.

Also opened at microsoft/vscode#101050 for the VS Code JSON editor extension

[apupier]

@JPinkney is there something to do on VS Code yaml or Yaml-language-server side? or it is relying on the VS Code Json/Json Language server for downloading the schemas?

[JPinkney]

On the yaml language server side we just grab the list of schemas and send them to be loaded. When they're loaded I believe its https://github.com/microsoft/vscode-json-languageservice/blob/908ede3fd3c3b1e1c2f5f9b96ad9c4056e8fb1d0/src/services/jsonSchemaService.ts#L360 that actually resolves the schema content