Move `get_config_dhcpinfo()` function into `src/dhcp/dhcp_config_utils.c`

[aloisklink]

In edgesec, we have two slightly different definitions of get_config_dhcpinfo(), in:

• https://github.com/nqminds/edgesec/blob/da4f33eb7377563e02b032398f52a4f21fc570a2/src/config.c#L32-L84
• https://github.com/nqminds/edgesec/blob/da4f33eb7377563e02b032398f52a4f21fc570a2/tests/dhcp/test_dnsmasq.c#L165-L221

This PR proposes replacing these two definitions with a single definition in a new file called src/dhcp/dhcp_config_utils.c.

Minor differences:

• I've taken the definition from the src/config.c file. The one in tests/dhcp/test_dnsmasq.c was almost exactly the same, except it had a bunch of log_trace() commands, which I removed.
• I've made the info parameter const since we only read from it.

[codecov[bot]]

Codecov Report

Merging #548 (803d702) into main (da4f33e) will decrease coverage by 0.03%. The diff coverage is 71.79%.

@@            Coverage Diff             @@
##             main     #548      +/-   ##
==========================================
- Coverage   54.14%   54.11%   -0.03%     
==========================================
  Files         144      145       +1     
  Lines       21043    20999      -44     
==========================================
- Hits        11394    11364      -30     
+ Misses       9649     9635      -14     

Impacted Files	Coverage Δ
src/config.c	79.65% <ø> (+0.60%)	:arrow_up:
tests/dhcp/test_dnsmasq.c	100.00% <ø> (+4.80%)	:arrow_up:
src/dhcp/dhcp_config_utils.c	71.79% <71.79%> (ø)

... and 2 files with indirect coverage changes

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