refactor: remove DIContainer abstraction

[Reasno]

This PR makes core tightly coupled to uber/dig. While this is counter-intuitive, the previous abstraction was very leaky. Most components implicitly depend on uber/dig specific features, such as dig.In, dig.Out and optional:"true" tags.

The rationale of this PR is: good abstraction > no abstraction > bad/leacky abstration.

After this change, the core and components are free to use uber/dig's advanced features. I expect this will make developer UX much better.

[codecov]

Codecov Report

Merging #196 (89c4384) into master (30380dd) will increase coverage by 0.00%.
The diff coverage is 88.88%.

@@           Coverage Diff           @@
##           master     #196   +/-   ##
=======================================
  Coverage   82.25%   82.25%           
=======================================
  Files          88       89    +1     
  Lines        3392     3409   +17     
=======================================
+ Hits         2790     2804   +14     
- Misses        448      450    +2     
- Partials      154      155    +1     

Impacted Files	Coverage Δ
ots3/uploader.go	85.85% <ø> (ø)
c.go	76.72% <70.00%> (-1.20%)	⬇️
di/optional_provider.go	87.50% <87.50%> (ø)
default_config.go	78.94% <100.00%> (ø)
di/populator.go	100.00% <100.00%> (ø)

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