Add client-side validations

[gadial]

Summary

This PR adds a new file, utils/validations.py and data validations which can be applied client-side to prevent the user from sending a job that will fail at a later stage.

Details and comments

The added validations:

1. In Sampler, no classical register of size 0 is passed.
2. In Sampler, classical register names are valid, non-keyword Python identifiers.
3. In Estimator, no empty observable array is passed.

[coveralls]

Pull Request Test Coverage Report for Build 9443329778

Details

• 25 of 25 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.05%) to 82.407%

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Totals
Change from base Build 9402463581:	0.05%
Covered Lines:	6061
Relevant Lines:	7355

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9569004723

Details

• 49 of 50 (98.0%) changed or added relevant lines in 10 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.06%) to 82.0%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit_ibm_runtime/utils/validations.py	37	38	97.37%

Totals
Change from base Build 9568868060:	0.06%
Covered Lines:	6077
Relevant Lines:	7411

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💛 - Coveralls