Replaced the static key-value attribute storage in update-form instruments
with sample-evaluated attributes, matching the log-record attr change.
The 'attr' keyword now accepts a key and a HAProxy sample expression
evaluated at runtime.
The struct (conf.h) changed from otelc_kv/attr_len to a list of
flt_otel_conf_sample entries. The parser (parser.c) calls
flt_otel_parse_cfg_sample() with n=1 per attr keyword. At runtime
(event.c) each attribute is evaluated via flt_otel_sample_eval() and
added via flt_otel_sample_add_kv() to a bare flt_otel_scope_data_kv,
which is passed to the meter.
Updated documentation, debug macro and test configurations.
Factored the sample evaluation logic out of flt_otel_sample_add() into a
new flt_otel_sample_eval() function that evaluates a sample definition
into an otelc_value. Both the log-format path and the bare sample
expression path are handled, with a flag_native parameter controlling
native type preservation for single-expression samples.
flt_otel_sample_add() now calls flt_otel_sample_eval() and dispatches the
result.
Made flt_otel_sample_add_kv() non-static so callers outside util.c can
add key-value pairs directly to a bare flt_otel_scope_data_kv without
requiring the full flt_otel_scope_data structure.
Added the full documentation set for the OpenTelemetry filter.
The main README served as the user-facing guide covering build
instructions, core OpenTelemetry concepts, the complete filter
configuration reference, usage examples with worked scenarios,
CLI commands, and known limitations.
Supplementary documents provided a detailed configuration guide with
worked examples (README-configuration), an internal C structure reference
for developers (README-conf), a function reference organized by source
file (README-func), an architecture and implementation review
(README-implementation), and miscellaneous notes (README-misc).
