meta/sql: retry transaction after too many connections

[davies]

close #916

[codecov-commenter]

Codecov Report

Merging #1876 (fefaa70) into main (85af540) will increase coverage by 0.10%.
The diff coverage is 25.00%.

@@            Coverage Diff             @@
##             main    #1876      +/-   ##
==========================================
+ Coverage   61.28%   61.39%   +0.10%     
==========================================
  Files         135      135              
  Lines       23410    23413       +3     
==========================================
+ Hits        14347    14374      +27     
+ Misses       7389     7371      -18     
+ Partials     1674     1668       -6     

Impacted Files	Coverage Δ
pkg/meta/sql.go	64.53% <25.00%> (+<0.01%)	⬆️
pkg/chunk/disk_cache.go	80.33% <0.00%> (+0.48%)	⬆️
pkg/vfs/writer.go	79.66% <0.00%> (+1.01%)	⬆️
pkg/vfs/reader.go	80.29% <0.00%> (+3.10%)	⬆️
pkg/chunk/utils_unix.go	93.33% <0.00%> (+20.00%)	⬆️

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