Fixes #40171. Bug not in any released Tor.

Found by coverity:

  *** CID 1468664:  Resource leaks  (RESOURCE_LEAK)
  /src/test/test_metrics.c: 83 in test_config()
  77       tt_int_op(ret, OP_EQ, false);
  78
  79      done:
  80       SMARTLIST_FOREACH(ports, port_cfg_t *, c, port_cfg_free(c));
  81       smartlist_free(ports);
  82       or_options_free(options);
  >>>     CID 1468664:  Resource leaks  (RESOURCE_LEAK)
  >>>     Variable "err_msg" going out of scope leaks the storage it points to.
  83     }
  84
  85     static char _c_buf[256];
  86     #define CONTAINS(conn, msg) \
  87       do { \
  88         tt_int_op(buf_datalen(conn->outbuf), OP_EQ, (strlen(msg))); \

Signed-off-by: David Goulet <dgoulet@torproject.org>

The "METRICS_PREFIX" was not expanded but rather used as a litteral. Fix that
by just removing the define and using "tor_" directly.

Reviewed-by: Alexander Færøy <ahf@torproject.org>
Signed-off-by: David Goulet <dgoulet@torproject.org>

Closes #40063

Signed-off-by: David Goulet <dgoulet@torproject.org>

Related to #40063

Signed-off-by: David Goulet <dgoulet@torproject.org>

Related to #40063

Signed-off-by: David Goulet <dgoulet@torproject.org>

Signed-off-by: David Goulet <dgoulet@torproject.org>

Signed-off-by: David Goulet <dgoulet@torproject.org>

Signed-off-by: David Goulet <dgoulet@torproject.org>

Signed-off-by: David Goulet <dgoulet@torproject.org>

Tracks the total number of established introduction circuit.

Related to #40063

Signed-off-by: David Goulet <dgoulet@torproject.org>

The total number of rendezvous circuit created and the number of established
ones which is a gauge that decreases to keep an updated counter.

Related to #40063

Signed-off-by: David Goulet <dgoulet@torproject.org>

Related to #40063

Signed-off-by: David Goulet <dgoulet@torproject.org>

Signed-off-by: David Goulet <dgoulet@torproject.org>

At this commit, a new service registers to the module and a store is created.
It also remove itself from the metrics module if it goes away.

In order to hook into the metrics subsystem, this commit attaches the HS
subsystem into the subsystem global list so its get_metrics() call can be
accessible.

HS initialization is still _not_ done through the subsys module as it is
likely require much more testing.

Related to #40063

Signed-off-by: David Goulet <dgoulet@torproject.org>

If MetricsPort is defined, listen on it and handle the incoming request.

Signed-off-by: David Goulet <dgoulet@torproject.org>

Related to #40063

Signed-off-by: David Goulet <dgoulet@torproject.org>

Used to provide an interface to create metrics store and update the entries.

Related to #40063

Signed-off-by: David Goulet <dgoulet@torproject.org>