mast import crashes when botocore optional dependency is not installed

[pllim]

To reproduce this problem:

1. Make sure botocore is not installed.
2. from astroquery.mast import Observations

astroquery/astroquery/mast/observations.py

Line 21 in a85d9e4

from botocore.exceptions import ClientError, BotoCoreError

It crashes with ModuleNotFoundError: No module named 'botocore' even though botocore is not required:

astroquery/pyproject.toml

Lines 58 to 64 in a85d9e4

	all = [
	"mocpy>=0.12",
	"astropy-healpix",
	"boto3",
	"botocore",
	"regions>=0.5",
	]

Desired outcome: It does not crash on import.

[snbianco]

Should be fixed with #3534

[bsipocz]

Should be fixed with #3534

I'm halfway through the review there, got bogged down in some of the try/excepts (and the unrelated fact that for testing we apparently always pulling in some of the cloud packages (which we definitely should never do).