Gracefully handle GCS default client error

[kaitj]

GCS default client setup can error out if dependencies is not available. This is currently only true because b2t can be installed with only the s3 dependency. S3 dependencies are always guranteed if s3 or cloud dependencies are installed

Closes #87

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
__init__.py	9	0	100%
__main__.py	69	8	88%	101, 110, 135, 137–138, 164, 168, 172
_entities.py	112	1	99%	129
_indexing.py	212	5	97%	150, 159–160, 409, 447
_logging.py	31	4	87%	30, 37, 39–40
_metadata.py	48	4	91%	39–40, 66, 71
_pathlib.py	21	5	76%	16–17, 19–20, 22
_version.py	11	0	100%
pybids
__init__.py	4	0	100%
_bidsfile.py	38	13	65%	71–73, 77–79, 83–85, 89–91, 95
_layout.py	156	45	71%	63, 72, 81, 104, 114–115, 118, 140–141, 156–157, 173–174, 177–181, 186, 188–189, 192–193, 228, 233, 241, 322–324, 389–394, 396, 399–404, 406, 462, 482
_utils.py	13	5	61%	47–50, 52
TOTAL	724	90	87%

Tests	Skipped	Failures	Errors	Time
100	1 💤	0 ❌	0 🔥	9.813s ⏱️

[kaitj]

Patch fixing error raised from cloud imports