Support configuration parameter extra_float_digits

[lmatz]

Describe the bug

SET extra_float_digits = 3;
unrecognized configuration parameter "extra_float_digits"

To Reproduce

Expected behavior
The same as PG.

Additional context

[lmatz]

postgresql.org/docs/current/datatype-numeric.html#DATATYPE-FLOAT

For compatibility with output generated by older versions of PostgreSQL, and to allow the output precision to be reduced, the extra_float_digits parameter can be used to select rounded decimal output instead. Setting a value of 0 restores the previous default of rounding the value to 6 (for float4) or 15 (for float8) significant decimal digits. Setting a negative value reduces the number of digits further; for example -2 would round output to 4 or 13 digits respectively.

Any value of extra_float_digits greater than 0 selects the shortest-precise format.

Applications that wanted precise values have historically had to set extra_float_digits to 3 to obtain them. For maximum compatibility between versions, they should continue to do so.

[lmatz]

My understanding is that setting to 3 for us is a no-op right now as we always output the shortest-precise format.

[liurenjie1024]

Should we close this issue now?