Add remote configuration changeset

[lloeki]

What does this PR do?

Add a reporting of which paths were touched, what the content was before and what it is after the transaction.

Motivation

Remote configuration.

Contrary to transactions which are a sequential list of operations to apply in order, for mutative usage internal to the repository, a changeset is a report of state change, for a consumer external to the repository (more precisely the upcoming dispatcher).

Additional Notes

Using an Array-based ContentList may not be the most optimal data structure. I am considering changing it to a Hash-based ContentMap instead in the future. Nonetheless, ContentList does the job for this PR.

How to test the change?

  require 'datadog/core/remote/configuration/path'
  require 'datadog/core/remote/configuration/target'
  require 'datadog/core/remote/configuration/content'

  path2 = Datadog::Core::Remote::Configuration::Path.parse('datadog/42/PRODUCT/bar/config')
  content2 = Datadog::Core::Remote::Configuration::Content.parse({path: 'datadog/42/PRODUCT/bar/config', content: StringIO.new('Lorem ipsum')})
  target2 = Datadog::Core::Remote::Configuration::Target.parse({'length' => 11, 'hashes' => {'sha256' => 'a9a66978f378456c818fb8a3e7c6ad3d2c83e62724ccbdea7b36253fb8df5edd'}})
  content3 = Datadog::Core::Remote::Configuration::Content.parse({path: 'datadog/42/PRODUCT/foo/config', content: StringIO.new('dolor sit amet')})
  target3 = Datadog::Core::Remote::Configuration::Target.parse({'length' => 11, 'hashes' => {'sha256' => 'aa8311d08b68a5fdda55ad0947fff3c5a4b2397f5f766e9c9a79f4a5486c633c'}})

  require 'datadog/core/remote/configuration/repository'

  repository = Datadog::Core::Remote::Configuration::Repository.new

  changes = repository.transaction do |repo, txn|
    txn.insert(path, target, content) # new => change
    txn.insert(path2, target2, content2) # new => change
    txn.set(targets_version: 42) # no path touched  => no change
    txn.update(path, target3, content3) # different => change
  end

  changes # should have 2 inserts, with content2 and content3

  changes = repository.transaction do |repo, txn|
    txn.update(path, target, content) # new => change
    txn.insert(path2, target2, content2) # already there => no change
  end

  changes # should have 1 update

  changes = repository.transaction do |repo, txn|
    txn.delete(path) # exists => change
  end

  changes # should have 1 delete

  changes = repository.transaction do |repo, txn|
    txn.delete(path) # absent => no change
  end
 
  changes # should have no delete

[codecov-commenter]

Codecov Report

Merging #2696 (7ccbbb1) into master (e0f9564) will increase coverage by 0.00%.
The diff coverage is 99.09%.

@@           Coverage Diff           @@
##           master    #2696   +/-   ##
=======================================
  Coverage   98.05%   98.06%           
=======================================
  Files        1208     1208           
  Lines       66246    66340   +94     
  Branches     2961     2969    +8     
=======================================
+ Hits        64960    65056   +96     
+ Misses       1286     1284    -2     

Impacted Files	Coverage Δ
...ib/datadog/core/remote/configuration/repository.rb	99.21% <97.95%> (-0.79%)	⬇️
lib/datadog/core/remote/configuration/content.rb	100.00% <100.00%> (ø)
.../datadog/core/remote/configuration/content_spec.rb	100.00% <100.00%> (ø)
...adog/core/remote/configuration/respository_spec.rb	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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