Add new optional data structure OP (optical profiles)

[chengdang]

Per request by CRTM users, we add a new optional data structure OP for the generic optical interface.

[chengdang]

A new optional data structure OP is added into CRTM.
OP contains optical data that needed for CRTM radiative transfer calculations.
By providing OP profiles, users may skip the traditional LUT-based aerosol/cloud simulations in CRTM.

  TYPE :: OP_Input_type
    ! Allocation indicator
    LOGICAL :: Is_Allocated = .FALSE.
    ! Release and version information
    INTEGER(Long) :: Release = OP_INPUT_RELEASE

    ! Dimensions
    INTEGER :: n_Channels         = 0  ! K dimension
    INTEGER :: n_Layers           = 0  ! L dimension
    INTEGER :: n_Phase_Elements   = 0  ! Ip dimension
    INTEGER :: n_Legendre_Terms   = 0  ! Il dimension
    
    ! Arrays
    REAL(fp), ALLOCATABLE :: tau(:,:)         ! K * L
    REAL(fp), ALLOCATABLE :: bs(:,:)          ! K * L
    REAL(fp), ALLOCATABLE :: kb(:,:)          ! K * L
    REAL(fp), ALLOCATABLE :: pcoeff(:,:,:,:)  ! K * L * Il * Ip

  END TYPE OP_Input_type

[chengdang]

Modules related to OP data structures are also added, including:

! ------------
! Visibilities
! ------------
PRIVATE
! Datatypes
PUBLIC :: OP_Input_type
! Operators
PUBLIC :: OPERATOR(==)
! Procedures
PUBLIC :: OP_Input_IsValid
PUBLIC :: OP_Input_Inspect
PUBLIC :: OP_Input_Create
PUBLIC :: OP_Input_Associated
PUBLIC :: OP_Input_InquireFile
PUBLIC :: OP_Input_ReadFile
PUBLIC :: OP_Input_WriteFile