Add remote configuration repository

[lloeki]

What does this PR do?

Add configuration repository, using PORO from #2687

Motivation

Additional Notes

This is an initial basic implementation. It is notably missing:

• storing digests for each bit of content
• reporting a summary of which paths have been updated and their corresponding data for taking action on the newly received configuration
• error tracking and reporting
• a content caching mechanism and cache state reporting

These will be added progressively.

How to test the change?

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

  path = Datadog::Core::Remote::Configuration::Path.parse('datadog/42/PRODUCT/foo/config')
  content = Datadog::Core::Remote::Configuration::Content.parse({path: 'datadog/42/PRODUCT/foo/config', content: StringIO.new('Lorem ipsum')})
  target = Datadog::Core::Remote::Configuration::Target.parse({'length' => 11, 'hashes' => {'sha256' => 'a9a66978f378456c818fb8a3e7c6ad3d2c83e62724ccbdea7b36253fb8df5edd'}})

  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'

  txn = Datadog::Core::Remote::Configuration::Repository::Transaction.new
  txn.delete(path)
  txn.operations

  txn = Datadog::Core::Remote::Configuration::Repository::Transaction.new
  txn.insert(path, target, content)
  txn.operations

  txn = Datadog::Core::Remote::Configuration::Repository::Transaction.new
  txn.update(path, target, content)
  txn.operations

  txn = Datadog::Core::Remote::Configuration::Repository::Transaction.new
  txn.set(opaque_backend_state: 'OPAQUE_DATA')
  txn.operations

  txn = Datadog::Core::Remote::Configuration::Repository::Transaction.new
  txn.set(targets_version: 42)
  txn.operations

  repository = Datadog::Core::Remote::Configuration::Repository.new
  repository.contents
  repository.root_version
  repository.targets_version

  repository.transaction do |repo, txn|
    txn.insert(path, target, content)
    txn.set(opaque_backend_state: 'OPAQUE_DATA', targets_version: target_map.version)
  end

  repository.contents
  repository.root_version
  repository.targets_version
  repository[path]

  repository.transaction do |repo, txn|
    txn.insert(path2, target2, content2)
  end

  repository[path2]
  repository.contents

  repository.transaction do |repo, txn|
    txn.insert(path, target, content)
  end

  repository.contents

  repository.transaction do |repo, txn|
    txn.update(path, target3, content3)
  end

  repository[path]

  repository.transaction do |repo, txn|
    txn.delete(path)
  end

  repository.contents
  repository[path]

  repository.transaction do |repo, txn|
    txn.update(path, target, content)
  end

  repository[path]

[lloeki]

Pending:

• specs
• RBS typing

[lloeki]

Rebased using git rebase --onto origin/add-remote-config-poro 37eb3b095 add-remote-config-repository

[lloeki]

Rebased using git rebase --onto master 414a626^ add-remote-config-repository

[lloeki]

Thanks for the specs and types! I have a suggestion concerning Base.

[codecov-commenter]

Codecov Report

Merging #2688 (bf7e2b2) into master (3ae66fb) will decrease coverage by 0.07%.
The diff coverage is 95.36%.

@@            Coverage Diff             @@
##           master    #2688      +/-   ##
==========================================
- Coverage   98.09%   98.03%   -0.07%     
==========================================
  Files        1168     1197      +29     
  Lines       64254    65714    +1460     
  Branches     2857     2926      +69     
==========================================
+ Hits        63033    64423    +1390     
- Misses       1221     1291      +70     

Impacted Files	Coverage Δ
lib/datadog/core/transport/http/builder.rb	79.01% <79.01%> (ø)
lib/datadog/core/transport/http.rb	79.66% <79.66%> (ø)
lib/datadog/core/transport/http/config.rb	84.55% <84.55%> (ø)
lib/datadog/core/transport/http/client.rb	87.50% <87.50%> (ø)
lib/datadog/core/transport/http/negotiation.rb	90.32% <90.32%> (ø)
spec/datadog/core/transport/integration_spec.rb	91.89% <91.89%> (ø)
lib/datadog/core/transport/http/api/instance.rb	93.75% <93.75%> (ø)
lib/datadog/core/transport/config.rb	96.00% <96.00%> (ø)
spec/datadog/tracing/contrib/roda/patcher_spec.rb	96.26% <96.26%> (ø)
lib/datadog/core/remote/configuration/target.rb	98.41% <98.41%> (ø)
... and 22 more

... and 1 file with indirect coverage changes

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