br: add more fields for merged backup SST (#1282)

* add sub_range_groups into backup request to mark the merged gap

Signed-off-by: Jianjun Liao <jianjun.liao@outlook.com>

* make go

Signed-off-by: Jianjun Liao <jianjun.liao@outlook.com>

* multi rewrite rules for one SST file

Signed-off-by: Jianjun Liao <jianjun.liao@outlook.com>

* add table checksums

Signed-off-by: Jianjun Liao <jianjun.liao@outlook.com>

* add table checksums

Signed-off-by: Jianjun Liao <jianjun.liao@outlook.com>

* rename from TableChecksum to TableMeta

Signed-off-by: Jianjun Liao <jianjun.liao@outlook.com>

* rename: add prefix sorted_

Signed-off-by: Jianjun Liao <jianjun.liao@outlook.com>

* add more annotations

Signed-off-by: Jianjun Liao <jianjun.liao@outlook.com>

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Signed-off-by: Jianjun Liao <jianjun.liao@outlook.com>
Co-authored-by: 山岚 <36239017+YuJuncen@users.noreply.github.com>