Automatically adjust `GOMEMLIMIT` for br clp

[Leavrth]

Enhancement

[Tristan1900]

I am reviewing the br: set memory limit PR and trying to understand the reason of doing this memory enhancement, could you add a few lines of description of why we are doing it? Thanks

[Leavrth]

I am reviewing the br: set memory limit PR and trying to understand the reason of doing this memory enhancement, could you add a few lines of description of why we are doing it? Thanks

There are too much temporary memory allocation during the backup/restore, such as download backupmeta including many tables' information(TableInfo), and unmarshal/marshal the TableInfo or statistic. So we need to set GOMEMLIMIT for the br binary process, otherwise these temporary memory cannot be GCed in time.

This PR will set the GOMEMLIMIT in default. If users are not satisfied with the default value, they can set it to override by:

GOMEMLIMIT=16GiB ./br restore full ...