refactor(otlp-transformer): re-structure package to prepare for separate entrypoints

[pichlermarc]

Which problem is this PR solving?

Important

This is a refactor, I only moved code, but the logic has not changed.

I'm planning to re-structure the exporters to have seperate entrypoints. This solves some issues with rollup, that warns even for code that is dead in the end-user's app. See #5216

The planned structure of the entrypoints for each signal is:

• /signal, /signal/protobuf, singal/json

To make this change easier to review, I've opened this PR, which just moves code into the correct place so that we can add the entypoints in #5263

Prepares for #5263

Type of change

• Internal Refactor

How Has This Been Tested?

• Unit tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.66%. Comparing base (6d31a18) to head (2bcd3b3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5264      +/-   ##
==========================================
- Coverage   94.67%   94.66%   -0.02%     
==========================================
  Files         315      322       +7     
  Lines        8057     8058       +1     
  Branches     1632     1632              
==========================================
  Hits         7628     7628              
- Misses        429      430       +1     

Files with missing lines	Coverage Δ
...l/packages/otlp-transformer/src/common/internal.ts	100.00% <100.00%> (ø)
...ntal/packages/otlp-transformer/src/common/utils.ts	100.00% <ø> (ø)
...ckages/otlp-transformer/src/logs/internal-types.ts	100.00% <ø> (ø)
...tal/packages/otlp-transformer/src/logs/internal.ts	100.00% <100.00%> (ø)
...l/packages/otlp-transformer/src/logs/json/index.ts	100.00% <100.00%> (ø)
...al/packages/otlp-transformer/src/logs/json/logs.ts	100.00% <100.00%> (ø)
...ckages/otlp-transformer/src/logs/protobuf/index.ts	100.00% <100.00%> (ø)
...ackages/otlp-transformer/src/logs/protobuf/logs.ts	100.00% <100.00%> (ø)
...ges/otlp-transformer/src/metrics/internal-types.ts	100.00% <ø> (ø)
.../packages/otlp-transformer/src/metrics/internal.ts	100.00% <100.00%> (ø)
... and 10 more

... and 1 file with indirect coverage changes