[PATCH] Memory leak in pg_config

Hi,

I've been trying to run Postgis regress tests under Clang sanitizers and one of
the issues I'm facing is the constant stream of errors during the `configure`
step coming from calls to `pg_config`.

Example:
```
$ pg_config --cc
clang

=================================================================
==14521==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 368 byte(s) in 1 object(s) allocated from:
    #0 0x55de20d161d9 in malloc (/usr/bin/pg_config+0xf81d9)
[...]

SUMMARY: AddressSanitizer: 2610 byte(s) leaked in 47 allocation(s).
```

The leaked memory is part of the `configdata` array which isn't freed before
exiting. It doesn't have any long term impact but it's annoying.

A similar thing happens in the `pg_config` SQL function. Since the memory
will be released at the end of the transaction, releasing it is optional but
I've done it anyway.

I'm attaching a the patch with the changes.

Greetings,

Greetings,

--
Raúl Marín Rodríguez
carto.com