refactor(api): restructured API for type safety, maintainability and docs generation

- These changes makes the API incombatible with previous versions
- Added new types for error handling, success responses, and health checks.
- Updated health check logic to utilize the new types for better clarity and structure.
- Refactored existing handlers to improve response consistency and error handling.
- Updated Makefile to include a new target for generating API types from Swagger.
- Updated "new agent" API to respond an encrypted cert pair

internal/api/v1/file/get.go

@@ -0,0 +1,73 @@
+package fileapi
+
+import (
+	"net/http"
+	"os"
+	"path"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+	apitypes "github.com/yusing/go-proxy/internal/api/types"
+	"github.com/yusing/go-proxy/internal/common"
+)
+
+type FileType string // @name FileType
+
+const (
+	FileTypeConfig     FileType = "config"     // @name FileTypeConfig
+	FileTypeProvider   FileType = "provider"   // @name FileTypeProvider
+	FileTypeMiddleware FileType = "middleware" // @name FileTypeMiddleware
+)
+
+type GetFileContentRequest struct {
+	FileType FileType `form:"type" binding:"required,oneof=config provider middleware"`
+	Filename string   `form:"filename" binding:"required" format:"filename"`
+} //	@name	GetFileContentRequest
+
+// @x-id				"get"
+// @BasePath		/api/v1
+// @Summary		Get file content
+// @Description	Get file content
+// @Tags			file
+// @Accept			json
+// @Produce		json,application/godoxy+yaml
+// @Param			query	query		GetFileContentRequest	true	"Request"
+// @Success		200			{string}	application/godoxy+yaml	"File content"
+// @Failure		400			{object}	apitypes.ErrorResponse
+// @Failure		403			{object}	apitypes.ErrorResponse
+// @Failure		500			{object}	apitypes.ErrorResponse
+// @Router			/file/content [get]
+func Get(c *gin.Context) {
+	var request GetFileContentRequest
+	if err := c.ShouldBindQuery(&request); err != nil {
+		c.JSON(http.StatusBadRequest, apitypes.Error("invalid request", err))
+		return
+	}
+
+	content, err := os.ReadFile(request.FileType.GetPath(request.Filename))
+	if err != nil {
+		c.Error(apitypes.InternalServerError(err, "failed to read file"))
+		return
+	}
+
+	// RFC 9512: https://www.rfc-editor.org/rfc/rfc9512.html
+	// xxx/yyy+yaml
+	c.Data(http.StatusOK, "application/godoxy+yaml", content)
+}
+
+func GetFileType(file string) FileType {
+	switch {
+	case strings.HasPrefix(path.Base(file), "config."):
+		return FileTypeConfig
+	case strings.HasPrefix(file, common.MiddlewareComposeBasePath):
+		return FileTypeMiddleware
+	}
+	return FileTypeProvider
+}
+
+func (t FileType) GetPath(filename string) string {
+	if t == FileTypeMiddleware {
+		return path.Join(common.MiddlewareComposeBasePath, filename)
+	}
+	return path.Join(common.ConfigBasePath, filename)
+}