feat: support custom request headers

[patrickdemers6]

Depending on the Trino server configuration, the ability to pass custom headers on a per-request is incredibly valuable. Transaction ID, instrumentation ID, and Authorization headers to name a few. This adds the ability to set custom headers using a sql.Named parameter where the name has the prefix X-Header-.

Testing

1. Unit test in trino_test.go.
2. Manually validated with a local Trino server.

I signed CLA earlier today but it may not be in the system yet.

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[cla-bot]

Thank you for your pull request and welcome to the Trino community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file. Continue to work with us on the review and improvements in this PR, and submit the signed CLA to [email protected]. Photos, scans, or digitally-signed PDF files are all suitable. Processing may take a few days. The CLA needs to be on file before we merge your changes. For more information, see https://github.com/trinodb/cla

[cla-bot]

Thank you for your pull request and welcome to the Trino community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file. Continue to work with us on the review and improvements in this PR, and submit the signed CLA to [email protected]. Photos, scans, or digitally-signed PDF files are all suitable. Processing may take a few days. The CLA needs to be on file before we merge your changes. For more information, see https://github.com/trinodb/cla

[nineinchnick]

There's a similar discussion in the main Trino repository: trinodb/trino#15826. I think it also applies here. I'd rather discuss specific use cases and keep Trino clients in multiple languages consistent.