Allow usage of byte arrays to set RootCAs

[sauttefk]

Something like this is now possible:

const size_t DST_Root_CA_X3_len = 846;
const uint8_t DST_Root_CA_X3[] = {0x30, ....., 0xfd}; 
client.setCACert(DST_Root_CA_X3, DST_Root_CA_X3_len);

[codecov-io]

Codecov Report

Merging #2968 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2968   +/-   ##
=======================================
  Coverage   27.82%   27.82%           
=======================================
  Files          20       20           
  Lines        3626     3626           
  Branches      656      656           
=======================================
  Hits         1009     1009           
  Misses       2441     2441           
  Partials      176      176

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