docs/google: Add missing "Required" tags
docs/google: Add missing "Required" tags

This change updates the password and username fields in the Master Auth subheading to include the "Required" tag.
ubschmidt2/terraform-provider-google,ubschmidt2/terraform-provider-google,terraform-providers/terraform-provider-google,nickithewatt/terraform-provider-google,rosbo/terraform-provider-google,rosbo/terraform-provider-google,nickithewatt/terraform-provider-google,drebes/terraform-provider-google,drebes/terraform-provider-google,terraform-providers/terraform-provider-google,hashicorp/terraform-provider-google,rosbo/terraform-provider-google,hashicorp/terraform-provider-google-beta,hashicorp/terraform-provider-google-beta,selmanj/terraform-provider-google,hashicorp/terraform-provider-google,selmanj/terraform-provider-google,terraform-providers/terraform-provider-google,hashicorp/terraform-provider-google-beta,drebes/terraform-provider-google,selmanj/terraform-provider-google,terraform-providers/terraform-provider-google,hashicorp/terraform-provider-google,rosbo/terraform-provider-google,ubschmidt2/terraform-provider-google,hashicorp/terraform-provider-google,nickithewatt/terraform-provider-google,drebes/terraform-provider-google,ubschmidt2/terraform-provider-google,hashicorp/terraform-provider-google-beta,terraform-providers/terraform-provider-google