bump version to 1.0.0-rc.4

[tsloughter]

The API Application no longer uses a VERSION file because mix.exs
grabs the version to use from the src/opentelemetry_api.app.src
file, so it is no longer needed.

The Exporter Application sets its version manually in .app.src
so that its versions can be tracked separately from the SDK.

[tsloughter]

Will wait for #332 before actually merging this and cutting releases.

[codecov]

Codecov Report

Merging #333 (75d0e82) into main (6585266) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #333      +/-   ##
==========================================
- Coverage   39.77%   39.75%   -0.03%     
==========================================
  Files          54       54              
  Lines        3653     3655       +2     
==========================================
  Hits         1453     1453              
- Misses       2200     2202       +2     

Flag	Coverage Δ
api	67.28% <ø> (ø)
elixir	16.44% <ø> (ø)
erlang	39.79% <ø> (-0.03%)	⬇️
exporter	19.98% <ø> (ø)
sdk	77.44% <ø> (-0.21%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
apps/opentelemetry/src/otel_simple_processor.erl	69.81% <0.00%> (-1.35%)	⬇️
apps/opentelemetry/src/otel_utils.erl	0.00% <0.00%> (ø)

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