Add Chuvash collation (utf8mb4_chuvash_ci) to Index.xml

Hello!

Currently, the Chuvash language (Cyrillic script) does not have native collation support in the server. As a result, specific Chuvash characters (Ӑ, Ӗ, Ҫ, Ӳ) are sorted incorrectly and end up at the very end of the alphabet (after 'Я').

To fix this, I would like to propose adding a native Chuvash collation `utf8mb4_chuvash_ci` to the `Index.xml` configuration file.

Below are the exact LDML XML rules that define the correct sorting order for the Chuvash alphabet. The specific characters are tailored to be sorted immediately after their base Cyrillic counterparts:

• Ӑ / ӑ after А / а
• Ӗ / ӗ after Е / е
• Ҫ / ҫ after С / с
• Ӳ / ӳ after У / у

Please consider adding this block to the `<charset name="utf8mb4">` section in `sql/share/charsets/Index.xml`:

  <collation name="utf8mb4_chuvash_ci" id="1040">

    <rules>

      <!-- Chuvash letter Ӑ/ӑ after А/а -->

      <reset>\u0410</reset>

      <shift>\u04D0</shift>

      <reset>\u0430</reset>

      <shift>\u04D1</shift>

      <!-- Chuvash letter Ӗ/ӗ after Е/е -->

      <reset>\u0415</reset>

      <shift>\u04D6</shift>

      <reset>\u0435</reset>

      <shift>\u04D7</shift>

      <!-- Chuvash letter Ҫ/ҫ after С/с -->

      <reset>\u0421</reset>

      <shift>\u04AA</shift>

      <reset>\u0441</reset>

      <shift>\u04AB</shift>

      <!-- Chuvash letter Ӳ/ӳ after У/у -->

      <reset>\u0423</reset>

      <shift>\u04F2</shift>

      <reset>\u0443</reset>

      <shift>\u04F3</shift>

    </rules>

  </collation>

Thank you for supporting language diversity in the database server!