Add UBX_MSG_RXM_RTCM to monitor RTCM stats

[AlexKlimaj]

This PR adds support for the UBX-RXM-RTCM message which gives feedback on whether the ublox module is using the RTCM data that is being sent to it.

nsh> gps status
INFO  [gps] Main GPS
INFO  [gps] protocol: UBX
INFO  [gps] status: OK, port: /dev/ttyS0, baudrate: 921600
INFO  [gps] sat info: disabled
INFO  [gps] rate reading:                  925 B/s
INFO  [gps] rate position:                1.00 Hz
INFO  [gps] rate velocity:                1.00 Hz
INFO  [gps] rate publication:             1.00 Hz
INFO  [gps] rate RTCM injection:         40.02 Hz
 sensor_gps
    timestamp: 244102098 (0.781204 seconds ago)
    timestamp_sample: 0
    time_utc_usec: 1684174039124558
    device_id: 11141125 (Type: 0xAA, SERIAL:0 (0x00))
    lat: 406203100
    lon: -1118287492
    alt: 1433548
    alt_ellipsoid: 1414764
    s_variance_m_s: 0.76600
    c_variance_rad: 2.39044
    eph: 6.32000
    epv: 10.58200
    hdop: 1.12000
    vdop: 1.75000
    noise_per_ms: 72
    jamming_indicator: 13
    vel_m_s: 0.18500
    vel_n_m_s: -0.00900
    vel_e_m_s: 0.18500
    vel_d_m_s: -0.06700
    cog_rad: 5.42557
    timestamp_time_relative: 0
    heading: nan
    heading_offset: -1.57080
    heading_accuracy: 0.00000
    rtcm_injection_rate: 40.01656
    automatic_gain_control: 0
    fix_type: 4
    jamming_state: 2
    spoofing_state: 1
    vel_ned_valid: True
    satellites_used: 11
    selected_rtcm_instance: 0
    rtcm_crc_failed: False
    rtcm_msg_used: 2