Added json options for nanostack heap statictics

[mikaleppanen]

Description

Added configuration options to mbed-mesh-api mbed_lib.json to enable nanostack nsdynmemLIB heap statistics.

This can be used on application to get memory statistics from nanostack heap.

Pull request type

[ ] Fix
[ ] Refactor
[ ] New target
[X] Feature
[ ] Breaking change

[mikaleppanen]

@artokin @kjbracey-arm Please review.

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2529
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7414/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2177
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7414/

[mbed-ci]

Test : SUCCESS

Build number : 2291
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7414/2291