Add support for role query parameters

[pulpdrew]

Summary

This PR adds support for specifying roles via request query parameters. Closes #269.

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

[CLAassistant]

All committers have signed the CLA.

[slvrtrn]

Thanks for the contribution! Tests are good, too. There is one thing that we should fix before merging (the example); the rest are mostly nitpicks

[slvrtrn]

The CLA also needs to be signed before we merge it.

[pulpdrew]

The CLA also needs to be signed before we merge it.

Will do - I am working with my company to make sure I am not violating any of their open source policies by signing, but will sign as soon as I have approval.

[slvrtrn]

@pulpdrew, do you have any updates regarding the CLA? I'd like to merge this, but non-signed CLA is a blocker.

[pulpdrew]

@pulpdrew, do you have any updates regarding the CLA? I'd like to merge this, but non-signed CLA is a blocker.

@slvrtrn Hey, apologies for the delay. My company is still reviewing the CLA. 🫠 They tell me they should have an update for me early next week. I will reply here with an ETA next week once I hear from them!

[pulpdrew]

@slvrtrn I have signed the CLA, thanks for waiting!