MINOR: sample: Add le2dec (little endian to decimal) sample fetch

MINOR: sample: Add le2dec (little endian to decimal) sample fetch

This commit introduces a sample fetch, `le2dec`, to convert
little-endian binary input samples into their decimal representations.
The function converts the input into a string containing unsigned
integer numbers, with each number derived from a specified number of
input bytes. The numbers are separated using a user-defined separator.

This new sample is achieved by adding a parametrized sample_conv_2dec
function, unifying the logic for be2dec and le2dec converters.

Co-authored-by: Christian Norbert Menges <christian.norbert.menges@sap.com>
[wt: tracked as GH issue #2915]
Signed-off-by: Willy Tarreau <w@1wt.eu>