Support configuring a CA certificates bundle and update to tokio-rustls 0.26.1

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The trust_cert_ca() config option configures one specific trusted CA certificate. However, there are two downsides:

• it requires a file path, so an in-memory certificate would have to be written to a temporary file
• it supports loading exactly one certificate, so if you need to load an entire bundle (e.g. the AWS RDS bundle) you're out of luck

The trust_cert_ca_bundle() method implemented here solves both of these issues by taking a bundle of PEM-encoded CA certificates in a Vec and adding all of them to the TLS context. For cases where a CA bundle needs to be loaded from disk, users can of course simply read the file on their end and pass the contents to trust_cert_ca_bundle.

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Hi, what's blocking this from getting merged?