fix(multipart): support multipart file inputs to non-file descriptors

[sauyon]

Fixes an oversight where if a user passed a multipart input with a filename to a descriptor that did not attempt to use request files, the descriptor would fail with a cryptic RuntimeError: Receive channel has not been made available.

[aarnphm]

ok I trust you with this

[sauyon]

I should test this ;)

[codecov]

Codecov Report

Merging #3005 (c2201fa) into main (616787a) will decrease coverage by 1.30%.
The diff coverage is 33.33%.

❗ Current head c2201fa differs from pull request most recent head efc24f0. Consider uploading reports for the commit efc24f0 to get more accurate results

@@            Coverage Diff             @@
##             main    #3005      +/-   ##
==========================================
- Coverage   70.61%   69.31%   -1.31%     
==========================================
  Files         104      104              
  Lines        9570     9568       -2     
==========================================
- Hits         6758     6632     -126     
- Misses       2812     2936     +124     

Impacted Files	Coverage Δ
bentoml/_internal/utils/formparser.py	18.96% <33.33%> (+0.25%)	⬆️
bentoml/_internal/utils/buildx.py	0.00% <0.00%> (-48.30%)	⬇️
bentoml/_internal/utils/docker.py	34.48% <0.00%> (-34.49%)	⬇️
bentoml/_internal/utils/platform.py	66.66% <0.00%> (-8.34%)	⬇️
bentoml/_internal/runner/container.py	83.98% <0.00%> (-6.07%)	⬇️
bentoml/_internal/runner/runner_handle/remote.py	82.82% <0.00%> (-6.07%)	⬇️
bentoml/_internal/resource.py	71.51% <0.00%> (-5.46%)	⬇️
bentoml/_internal/utils/uri.py	84.21% <0.00%> (-5.27%)	⬇️
bentoml/_internal/utils/telemetry.py	88.46% <0.00%> (-3.85%)	⬇️
bentoml/_internal/runner/utils.py	86.88% <0.00%> (-3.28%)	⬇️
... and 4 more

[sauyon]

I opened #3006, remind me to do that after your e2e changes go in @aarnphm