Deprecation of ChatModes are not Agents

[cicorias]

This setting is deprecated and will be removed in future releases. Chat modes are now called custom agents and are located in `.github/agents`

[WilliamBerryiii]

We have been working with the VSCode team on this issue for a while and will have update on it next week. We have received agreement that the capability would not be deprecated until a suitable replacement has been made available for agents. For now all agents must remain classified as chatmodes until the final prompt library import capability is in VSCode main.

I'll leave this issue open for those that run into this concern and will close when we have resolution.

[cicorias]

i'm so tempted to close it

[WilliamBerryiii]

DON'T! THIS WILL LIVE ON!!! At least until we can make sure DevDiv actually delivers on their promise! 🤣