Merge blueprint vendor data

[andrei-toterman]

This PR makes it so that cloud-init vendor data coming from a blueprint is merged with the vendor data that we normally provide. The merging follows these rules:

• If a key refers to a scalar value in both our vendor data and the blueprint vendor data, the blueprint is rejected
• If a key refers to values of different types in our vendor data and the blueprint vendor data, the blueprint is rejected
• If an entry from the blueprint vendor data does not exist in our own vendor data, simply add it
• If a key refers to a sequence in both our vendor data and the blueprint vendor data, append the items from the blueprint sequence to the sequence from our data
• If a key refers to a map in both our vendor data and the blueprint vendor data, recurse this algorithm on each key from the blueprint map

Fixes #3247

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (4ec525d) 84.01% compared to head (1149311) 84.02%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3315      +/-   ##
==========================================
+ Coverage   84.01%   84.02%   +0.01%     
==========================================
  Files         250      250              
  Lines       13487    13503      +16     
==========================================
+ Hits        11331    11346      +15     
- Misses       2156     2157       +1     

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[townsend2010]

Hey @andrei-toterman!

Thanks for this. LGTM and works as advertised!