feat: add trainer service to rpc package

[gaius-qi]

Description

• Add trainer service to rpc package

Related Issue

Motivation and Context

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Merging #2209 (6e5bb40) into main (cd94e99) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #2209      +/-   ##
==========================================
+ Coverage   49.44%   49.47%   +0.02%     
==========================================
  Files         141      141              
  Lines       19200    19200              
==========================================
+ Hits         9494     9499       +5     
+ Misses       9117     9114       -3     
+ Partials      589      587       -2     

Flag	Coverage Δ
Object-compatibility-e2etests	?
e2etests	?
unittests	49.47% <ø> (+0.02%)	⬆️

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see 3 files with indirect coverage changes