core: fix crash when running dry test mode (fluent#8872)

The tls variable for out_flush_params is not initialized as the
flb_start function is not called during the dry run. Call flb_init
directly and then shutdown the engine.

configuration test is successful
=================================================================
==63633==ERROR: AddressSanitizer: attempting free on address which was not malloc()-ed: 0x0001f71b3ac0 in thread T0
    #0 0x103c9f260 in wrap_free+0x98 (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x53260)
    #1 0x100179d9c in flb_free flb_mem.h:127
    #2 0x10017f4a0 in flb_output_exit flb_output.c:481
    #3 0x1001cb038 in flb_engine_shutdown flb_engine.c:1119
    #4 0x10010d45c in flb_destroy flb_lib.c:240
    #5 0x100008c40 in flb_main fluent-bit.c:1348
    #6 0x10000c644 in main fluent-bit.c:1456
    #7 0x18f11e0dc  (<unknown module>)

frame #6: 0x000000010017f4a4 fluent-bit`flb_output_exit(config=0x0000000102b00200) at flb_output.c:481:9
   478
   479 	    params = FLB_TLS_GET(out_flush_params);
   480 	    if (params) {
-> 481 	        flb_free(params);
   482 	    }
   483 	}

Signed-off-by: Holger Hans Peter Freyther <holger@freyther.de>

src/fluent-bit.c

@@ -1344,6 +1344,7 @@ int flb_main(int argc, char **argv)
 
     if (config->dry_run == FLB_TRUE) {
         fprintf(stderr, "configuration test is successful\n");
+        flb_init_env();
         flb_cf_destroy(cf_opts);
         flb_destroy(ctx);
         exit(EXIT_SUCCESS);