Refactoring request schemas

[joshSi]

Hi there!

I noticed a seeming inconsistency regarding OpenAI schemas in LocalAI and how they are defined/handled

OpenAI's tts endpoints are in localai.go, rather than openai.go as I'd expect:

LocalAI/core/schema/localai.go

Lines 17 to 22 in e8f02c0

	type TTSRequest struct {
	Model string `json:"model" yaml:"model"`
	Input string `json:"input" yaml:"input"`
	Voice string `json:"voice" yaml:"voice"`
	Backend string `json:"backend" yaml:"backend"`
	}

Meanwhile, the OpenAIRequestStruct is reused in both chat and image endpoints, which is the root cause for #1910

LocalAI/core/schema/openai.go

Lines 108 to 154 in e8f02c0

	type OpenAIRequest struct {
	PredictionOptions
	Context context.Context `json:"-"`
	Cancel context.CancelFunc `json:"-"`
	// whisper
	File string `json:"file" validate:"required"`
	//whisper/image
	ResponseFormat ChatCompletionResponseFormat `json:"response_format"`
	// image
	Size string `json:"size"`
	// Prompt is read only by completion/image API calls
	Prompt interface{} `json:"prompt" yaml:"prompt"`
	// Edit endpoint
	Instruction string `json:"instruction" yaml:"instruction"`
	Input interface{} `json:"input" yaml:"input"`
	Stop interface{} `json:"stop" yaml:"stop"`
	// Messages is read only by chat/completion API calls
	Messages []Message `json:"messages" yaml:"messages"`
	// A list of available functions to call
	Functions []grammar.Function `json:"functions" yaml:"functions"`
	FunctionCall interface{} `json:"function_call" yaml:"function_call"` // might be a string or an object
	Tools []grammar.Tool `json:"tools,omitempty" yaml:"tools"`
	ToolsChoice interface{} `json:"tool_choice,omitempty" yaml:"tool_choice"`
	Stream bool `json:"stream"`
	// Image (not supported by OpenAI)
	Mode int `json:"mode"`
	Step int `json:"step"`
	// A grammar to constrain the LLM output
	Grammar string `json:"grammar" yaml:"grammar"`
	JSONFunctionGrammarObject *grammar.JSONFunctionStructure `json:"grammar_json_functions" yaml:"grammar_json_functions"`
	Backend string `json:"backend" yaml:"backend"`
	// AutoGPTQ
	ModelBaseName string `json:"model_base_name" yaml:"model_base_name"`
	}

I propose refactoring these files by moving the tts struct out of localai.go, and creating a new file/struct for each of these endpoints that extends base type OpenAIRequestStruct, and maybe goes into a new file, something like core/schema/openai/image.go,core/schema/openai/tts.go, core/schema/openai/chat.go etc.

That said, it probably isn't that trivial of a refactoring