Enable architecture selection for DPCTL_TARGET_CUDA

[vlad-perevezentsev]

This PR proposes to change DPCTL_TARGET_CUDA CMake option from a boolean to a string allowing users to specify a CUDA architecture (e.g. sm_80). If not specified, it defaults to sm_50.

$ python scripts/build_locally.py --verbose --cmake-opts="-DDPCTL_TARGET_CUDA=<cuda_arch>"
# or
$ python scripts/build_locally.py --verbose --cmake-opts="-DDPCTL_TARGET_CUDA=ON"

The specified architecture is used to construct a SYCL alias target (e.g. nvidia_gpu_sm_80) and passed via -fsycl-targets option, following OneAPI for NVIDIA GPUs

Additionally removing DPCTL_TARGET_CUDA env handling logic

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[github-actions]

Deleted rendered PR docs from intelpython.github.com/dpctl, latest should be updated shortly. 🤞

[github-actions]

Array API standard conformance tests for dpctl=0.21.0dev0=py310h93fe807_8 ran successfully.
Passed: 1115
Failed: 6
Skipped: 119

[coveralls]

coverage: 84.972% (-0.02%) from 84.989%
when pulling 5bf20fd on update_cuda_build
into 35a8c26 on master.

[github-actions]

Array API standard conformance tests for dpctl=0.21.0dev0=py310h93fe807_9 ran successfully.
Passed: 1114
Failed: 7
Skipped: 119

[github-actions]

Array API standard conformance tests for dpctl=0.21.0dev0=py310h93fe807_10 ran successfully.
Passed: 1114
Failed: 7
Skipped: 119

[github-actions]

Array API standard conformance tests for dpctl=0.21.0dev0=py310h93fe807_17 ran successfully.
Passed: 1113
Failed: 8
Skipped: 119

[github-actions]

Array API standard conformance tests for dpctl=0.21.0dev0=py310h93fe807_22 ran successfully.
Passed: 1115
Failed: 6
Skipped: 119

[github-actions]

Array API standard conformance tests for dpctl=0.21.0dev0=py310h93fe807_30 ran successfully.
Passed: 1115
Failed: 6
Skipped: 119

[ndgrigorian]

LGTM

[github-actions]

Array API standard conformance tests for dpctl=0.21.0dev0=py310h93fe807_34 ran successfully.
Passed: 1115
Failed: 6
Skipped: 119

[github-actions]

Array API standard conformance tests for dpctl=0.21.0dev0=py310h93fe807_37 ran successfully.
Passed: 1114
Failed: 7
Skipped: 119