refactor: make global config an `AttrDict`

[P403n1x87]

This change refactors the global configuration object to be a subclass of the AttrDict object. The latter has also been refactored to allow more reliable attribute access in both an object and dict-like fashion. The DefaultAttrDict subclass of AttrDict has also been added to provide an analogue of defaultdict. The API of the global configuration class has been enlarged with a method that allows registering sub-configuration items for components using a namespace mechanism. This allows for the whole configuration to be reached from a single object while keeping coupling between components as loose as possible.

Checklist

• [ ] Added to the correct milestone.
• [ ] Tests provided or description of manual testing performed is included in the code or PR.
• [ ] Library documentation is updated.
• [ ] Corp site documentation is updated (link to the PR).

[P403n1x87]

For the time being we can take the "component" bit out and keep the rest of the changes

[majorgreys]

Discussed offline to remove the component change here and focus this refactor on not subclassing dict.

[codecov-commenter]

Codecov Report

Merging #3698 (bd4cacb) into 1.x (5731586) will decrease coverage by 0.02%. The diff coverage is 54.92%.

@@            Coverage Diff             @@
##              1.x    #3698      +/-   ##
==========================================
- Coverage   77.51%   77.49%   -0.03%     
==========================================
  Files         664      664              
  Lines       51039    51074      +35     
==========================================
+ Hits        39565    39579      +14     
- Misses      11474    11495      +21     

Impacted Files	Coverage Δ
ddtrace/internal/safety.py	0.00% <0.00%> (ø)
tests/internal/test_safety.py	0.00% <0.00%> (ø)
ddtrace/internal/utils/attrdict.py	100.00% <100.00%> (ø)
ddtrace/settings/config.py	91.52% <100.00%> (-0.22%)	:arrow_down:
ddtrace/settings/integration.py	92.72% <100.00%> (ø)
tests/tracer/test_settings.py	98.26% <100.00%> (+<0.01%)	:arrow_up:

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[mergify[bot]]

@P403n1x87 this pull request is now in conflict 😩

[mergify[bot]]

@P403n1x87 this pull request is now in conflict 😩

[brettlangdon]

This PR has been open for almost a year, and last changes were from 9 months ago. Closing for now, @P403n1x87 feel free to resolve conflicts and re-open!