API endpoint to create workspace prompt (custom context/instruction)

[alex-mcgovern]

The functionality for letting a user create custom prompts is already implemented in #643

All that seems to be missing is exposing a POST endpoint (for the dashboard to use) to allow setting a prompt without using the LLM/CLI. It should be a simple wrapper around update_workspace_system_prompt

codegate/src/codegate/workspaces/crud.py

Lines 82 to 97 in c140e65

	async def update_workspace_system_prompt(
	self, workspace_name: str, sys_prompt_lst: List[str]
	) -> Workspace:
	selected_workspace = await self._db_reader.get_workspace_by_name(workspace_name)
	if not selected_workspace:
	raise WorkspaceDoesNotExistError(f"Workspace {workspace_name} does not exist.")
	system_prompt = " ".join(sys_prompt_lst)
	workspace_update = Workspace(
	id=selected_workspace.id,
	name=selected_workspace.name,
	system_prompt=system_prompt,
	)
	db_recorder = DbRecorder()
	updated_workspace = await db_recorder.update_workspace(workspace_update)
	return updated_workspace