s1meta doesn't have Doppler Centroid Estimate (DCE) annotations

[agrouaze]

Sentinel-1 Level-1 data contains annotations describing doppler centroid estimates:

<dopplerCentroid>
    <dcEstimateList count="11">
      <dcEstimate>
        <azimuthTime>2021-01-02T16:31:42.605268</azimuthTime>
        <t0>5.372393076235181e-03</t0>
        <geometryDcPolynomial count="3">3.312591e+00 -4.573639e+01 -4.214722e+04</geometryDcPolynomial>
        <dataDcPolynomial count="3">-2.451500e+01 7.889123e+04 -6.537741e+07</dataDcPolynomial>
        <dataDcRmsError>1.056231975555420e+01</dataDcRmsError>
        <dataDcRmsErrorAboveThreshold>false</dataDcRmsErrorAboveThreshold>
        <fineDceAzimuthStartTime>2021-01-02T16:31:41.216615</fineDceAzimuthStartTime>
        <fineDceAzimuthStopTime>2021-01-02T16:31:43.993922</fineDceAzimuthStopTime>
        <fineDceList count="20">
          <fineDce>
            <slantRangeTime>5.685250085938474e-03</slantRangeTime>
            <frequency>-1.936767959594727e+01</frequency>
          </fineDce>

These informations are usefull to perform a chirp deramping on SLC products for instance. The mapping of such information has been done in PR #38 but will be done in a specific PR to ease the integration/review.

[agrouaze]

issue closed with #51