In a shared system many developers log as much as they
want into DLT. This can lead into overloading the logging
system resulting in bad performance and dropped logs.
This commit introduces trace load limits to restrict
applications to a certain log volume measured in bytes/s.
It is based on COVESA#134 but extends this heavily.

Trace load limits are configured via a space separted
configuraiton file.
The format of the file follows:

APPID [CTXID] SOFT_LIMIT HARD_LIMIT
The most matching entry will be selected for each log, meaning that
either app and context must match or at least the app id, for which a
default is created when not configured.
This allows to configure trace load for single contexts which can be
used for example to limit different applications in the qnx slog to a
given budget without affecting others or to give a file transfer
unlimited bandwidth.
It is recommended to always specify a budget for the application id
without the contexts to ensure new contexts and internal logs like DLTL
can be logged.

Applications are starting up with a default limit defined
via CMake variables TRACE_LOAD_USER_HARD_LIMIT, TRACE_LOAD_USER_SOFT_LIMIT.
As soon as the connection to the daemon was succesull each configuration
entry matching the app id will be sent to the client via an
application message.
If no configuration is found TRACE_LOAD_DAEMON_HARD_LIMIT and
TRACE_LOAD_USER_SOFT_LIMIT will be used instead.
The two staged configuration process makes sure that the daemon default
can be set to 0, forcing developers to define a limit for their
application while making sure that applications are able to log before
they received the log levels.

Measuring the trace load is done in the daemon and the client.
Dropping messages on the client side is the primary mechanism and
prevents sending logs to the daemon only to be dropped there, which
reduces the load of the IPC. Measuring again on daemon side makes
sure that rouge clients are still limited to the trace load defined.

Exceeding the limit soft will produce the following logs:
ECU1- DEMO DLTL log warn V 1 [Trace load exceeded trace soft limit on apid: DEMO. (soft limit: 2000 bytes/sec, current: 2414 bytes/sec)]
ECU1- DEMO DLTL log warn V 1 [Trace load exceeded trace soft limit on apid: DEMO, ctid TEST.(soft limit: 150 bytes/sec, current: 191 bytes/sec)]

Exceeding the hard limit will produce the same message but the text
'42 messages discarded.' is appended and messages will be dropped.
Dropped messages are lost and cannot be recovered, which forces
developers to get their logging volume under control.

As debug and trace load are usually disabled for production and thus do
not impact the performance of actual systems these logs are not
accounted for in trace load limits. In practice this turned out to be
very usefull to improve developer experience while maintaining good
performance, as devs know that debug and trace logs are only available
during development and important information has to be logged on a
higher level.

To simplify creating a trace limit base line the script
'utils/calculate-load.py' is provided which makes suggestions
for the limits based on actual log volume.

Signed-off-by: Alexander Mohr <alexander.m.mohr@mercedes-benz.com>

* Add documentation
* remove broken statistics
* set defaults for unit tests differently.

Signed-off-by: Alexander Mohr <alexander.m.mohr@mercedes-benz.com>

Signed-off-by: Alexander Mohr <alexander.m.mohr@mercedes-benz.com>

Signed-off-by: Alexander Mohr <alexander.m.mohr@mercedes-benz.com>