update pydicom reader to enable gpu load

[yiheng-wang-nv]

Related to #8241 .

Description

A few sentences describing the changes proposed in this pull request.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[yiheng-wang-nv]

I converted the decathlon task 03 liver data into .dcm format, and check the performance. Results are shown in the attach csv file.

Hi @ericspod @KumoLiu , this PR is ready, could you help to review it? Thanks!
acceleration_results.csv

[ericspod]

@yiheng-wang-nv I've added your csv data here, looks good to me!

filename	load_time_cpu	load_time_gpu	acceleration
liver_94.dcm	1.7886385060846806	1.1626716163009403	0.34996836289406413
liver_116.dcm	2.039297640323639	1.459715086966753	0.2842069455172348
liver_87.dcm	1.7027553180232644	1.1232791505753994	0.3403167567966144
liver_27.dcm	1.6333664860576391	1.0772031154483557	0.34050127473330394
liver_108.dcm	1.6188480481505394	1.0643940074369311	0.3424991254411104
liver_18.dcm	1.5974448192864656	1.053323021158576	0.340620090007825
liver_115.dcm	1.6150273736566303	1.0540638836100698	0.34733992698617044
liver_4.dcm	1.633006169460714	1.0484525095671415	0.3579616971604071
liver_117.dcm	1.5890469942241907	1.0437701912596822	0.34314705917852684
liver_113.dcm	1.5998324789106846	1.0554076870903373	0.3403011246471522