…ghten test (#13315)

Three follow-ups to #13146 (which started coercing additional_attributes
values to strings before sending them to OTel attr.string):

1. inject_attributes() gated insertion on `if val then`, which silently
   drops boolean false (Lua falsy) — regressing any user whose nginx
   variable resolves to a boolean false flag. Switch to
   `if val ~= nil then` so false survives.

2. ngx.req.get_headers() returns a Lua table for multi-value headers
   (e.g. multiple Set-Cookie / X-Forwarded-For entries). tostring()
   over a table emits 'table: 0x...' and that's what was landing in
   the span attribute. Extract a coerce_attr_value() helper that joins
   multi-value entries with ', ' and skips when the source is missing
   entirely.

3. TEST 22's response_body regex was qr/.*opentelemetry-lua.*/ which
   matches the OTLP exporter marker even when the numeric attributes
   are entirely absent from the export — i.e. the test would still
   pass with the regression #13146 was supposed to fix. Tighten it to
   assert each of request_time / bytes_sent appears as a stringValue.
   (upstream_response_time is intentionally not asserted: TEST 21
   serves /opentracing directly without proxying, so
   $upstream_response_time is nil and the plugin correctly omits the
   attribute.)

Signed-off-by: Shreemaan Abhishek <[email protected]>
Signed-off-by: Abhishek Choudhary <[email protected]>

…ache#13146)

…ghten test (apache#13315)

Three follow-ups to apache#13146 (which started coercing additional_attributes
values to strings before sending them to OTel attr.string):

1. inject_attributes() gated insertion on `if val then`, which silently
   drops boolean false (Lua falsy) — regressing any user whose nginx
   variable resolves to a boolean false flag. Switch to
   `if val ~= nil then` so false survives.

2. ngx.req.get_headers() returns a Lua table for multi-value headers
   (e.g. multiple Set-Cookie / X-Forwarded-For entries). tostring()
   over a table emits 'table: 0x...' and that's what was landing in
   the span attribute. Extract a coerce_attr_value() helper that joins
   multi-value entries with ', ' and skips when the source is missing
   entirely.

3. TEST 22's response_body regex was qr/.*opentelemetry-lua.*/ which
   matches the OTLP exporter marker even when the numeric attributes
   are entirely absent from the export — i.e. the test would still
   pass with the regression apache#13146 was supposed to fix. Tighten it to
   assert each of request_time / bytes_sent appears as a stringValue.
   (upstream_response_time is intentionally not asserted: TEST 21
   serves /opentracing directly without proxying, so
   $upstream_response_time is nil and the plugin correctly omits the
   attribute.)

Signed-off-by: Shreemaan Abhishek <[email protected]>
Signed-off-by: Abhishek Choudhary <[email protected]>