fix: install transformers for executor docker images

[ZiniuYu]

This pr installs the missing transformers package for torch & onnx executor docker images in hubble so that users can use M-CLIP models.

It also updates the hubble executor readme.

[codecov]

Codecov Report

Merging #851 (ab2ffa8) into main (4fcbf68) will decrease coverage by 10.77%.
The diff coverage is n/a.

❗ Current head ab2ffa8 differs from pull request most recent head ff308f0. Consider uploading reports for the commit ff308f0 to get more accurate results

@@             Coverage Diff             @@
##             main     #851       +/-   ##
===========================================
- Coverage   81.39%   70.61%   -10.78%     
===========================================
  Files          21       21               
  Lines        1596     1596               
===========================================
- Hits         1299     1127      -172     
- Misses        297      469      +172     

Flag	Coverage Δ
cas	70.61% <ø> (-10.78%)	⬇️

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Impacted Files	Coverage Δ
server/clip_server/executors/clip_tensorrt.py	0.00% <0.00%> (-93.11%)	⬇️
server/clip_server/model/clip_trt.py	0.00% <0.00%> (-85.72%)	⬇️
server/clip_server/model/trt_utils.py	0.00% <0.00%> (-83.52%)	⬇️

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[numb3r3]

LGTM