message: [gatsby-plugin-vercel-builder] support `trailingSlash` configuration
  Connects the gatsby trailingslash configuration property to our BOA3
  trailingslash property
diff: @@ -2,6 +2,7 @@ import type {
  IGatsbyPage,
  IGatsbyFunction,
  IRedirect,
  + IGatsbyConfig,
  } from 'gatsby/dist/redux/types';
  import Ajv, { JSONSchemaType } from 'ajv';
  @@ -24,6 +25,7 @@ export interface GatsbyState {
  pages: Array<[string, GatsbyPage]>;
  redirects: Array<GatsbyRedirect>;
  functions: Array<GatsbyFunction>;
  + config: GatsbyConfig;
  }
  export type GatsbyFunction = Pick<
  @@ -53,6 +55,19 @@ const GatsbyRedirectSchema: JSONSchemaType<GatsbyRedirect> = {
  required: ['fromPath', 'toPath'],
  } as const;
  +export type GatsbyConfig = Pick<IGatsbyConfig, 'trailingSlash'>;
  +
  +const GatsbyConfigSchema: JSONSchemaType<GatsbyConfig> = {
  + type: 'object',
  + properties: {
  + trailingSlash: {
  + type: 'string',
  + enum: ['always', 'never', 'ignore', 'legacy'],
  + nullable: true,
  + },
  + },
  +} as const;
  +
  const GatsbyStateSchema: JSONSchemaType<GatsbyState> = {
  type: 'object',
  properties: {
  @@ -73,8 +88,9 @@ const GatsbyStateSchema: JSONSchemaType<GatsbyState> = {
  type: 'array',
  items: GatsbyFunctionSchema,
  },
  + config: GatsbyConfigSchema,
  },
  - required: ['pages', 'redirects', 'functions'],
  + required: ['pages', 'redirects', 'functions', 'config'],
  additionalProperties: true,
  } as const;
  