Add remote configuration client

[lloeki]

What does this PR do?

Implement the remote configuration client class.

Motivation

Remote configuration

Additional Notes

Barebones implementation, some questions remain to be solved:

• there is AppSec-specific code in there (products and capabilities declaration)
• the callback system is missing because the repository does not yet report changes
• caching is not handled

There is an issue where the backend appears not to report any client_configs nor target_files, and targets may have targets but they may not correspond and/or include to the active client id.

In such gases, calling client.sync multiple times ends up getting the configuration. At this stage it is unknown whether this is expected API endpoint behaviour (e.g a delay in creating entries for a new client id, a "data lag" inside the agent...)

How to test the change?

  require 'ddtrace'

  Datadog.configure do |c|
    c.agent.host = '192.168.135.133'
    #c.tracing.enabled = true
    #c.diagnostics.debug = true
  end

  transport_options = {
    agent_settings: Datadog::Core::Configuration::AgentSettingsResolver.call(
      Datadog.configuration
    )
  }

  require 'datadog/core/transport/http'

  transport_v7 = Datadog::Core::Transport::HTTP.v7(**transport_options.dup)

  require 'datadog/core/remote/client'

  client = Datadog::Core::Remote::Client.new(transport_v7)
  repository = client.instance_eval { @repository }

  client.sync
  
  repository.contents

[lloeki]

Pending:

• specs
• RBS typing

[lloeki]

• Rebased using git rebase --onto origin/add-remote-config-repository 414a6260c add-remote-config-client
• Fixed usage of ContentList#find which was renamed to #find_content

[lloeki]

Rebased using git rebase --onto add-remote-config-repository c9ef278c6^ add-remote-config-client

[GustavoCaso]

Rebased using git rebase master

[codecov-commenter]

Codecov Report

Merging #2689 (5220533) into master (a692552) will increase coverage by 0.00%.
The diff coverage is 99.51%.

@@           Coverage Diff            @@
##           master    #2689    +/-   ##
========================================
  Coverage   98.03%   98.03%            
========================================
  Files        1197     1200     +3     
  Lines       65714    65915   +201     
  Branches     2926     2934     +8     
========================================
+ Hits        64420    64622   +202     
+ Misses       1294     1293     -1     

Impacted Files	Coverage Δ
lib/datadog/core/transport/http/config.rb	84.25% <90.00%> (-0.31%)	⬇️
lib/datadog/core/remote/client.rb	100.00% <100.00%> (ø)
lib/datadog/core/remote/configuration.rb	100.00% <100.00%> (ø)
lib/datadog/core/transport/config.rb	96.29% <100.00%> (+0.29%)	⬆️
spec/datadog/core/remote/client_spec.rb	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes

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[lloeki]

I guess we could improve this untyped given that we expect only a specific set of types here.

[GustavoCaso]

Sounds good. We can tackle that on a follow up PR