[rest] add mleid ip address API

[OmegaRelay]

We'd like to add a small PR to add functionality to retrieve the current mleid IP address of the border router over rest API. This PR adds a new endpoint /node/ip-address/mleid which only accepts GET requests and responds with the mleid ip address string.

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[wgtdkp]

Hi @OmegaRelay Thanks for contribution! What's the specific use case for ML-EID? Why not returning the OMR address which is externally routable or all the addresses?

[codecov]

Codecov Report

Attention: Patch coverage is 7.14286% with 13 lines in your changes missing coverage. Please review.

Project coverage is 43.38%. Comparing base (2b41187) to head (1a202a4).
Report is 975 commits behind head on main.

Files with missing lines	Patch %	Lines
src/rest/resource.cpp	7.14%	13 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2758       +/-   ##
===========================================
- Coverage   55.77%   43.38%   -12.39%     
===========================================
  Files          87      110       +23     
  Lines        6890    13405     +6515     
  Branches        0      956      +956     
===========================================
+ Hits         3843     5816     +1973     
- Misses       3047     7279     +4232     
- Partials        0      310      +310     

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[OmegaRelay]

Hi @OmegaRelay Thanks for contribution! What's the specific use case for ML-EID? Why not returning the OMR address which is externally routable or all the addresses?

Hi @wgtdkp, I only added support for MLEID as that's what we need in our application for network service discovery. I would be happy to expand it to support all ip addresses if that's preferred?