Support for Amazon Bedrock (Claude Sonnet 3.5)

[renebrandel]

This PR allows customers to use Claude Engineer with their AWS account. In work environments, developers might not have access to an Anthropic API Key locally but they'll have access to an AWS account with Amazon Bedrock access.

If the Anthropic API Key is not present, then Claude Engineer will connect to Anthropic Claude's model via Amazon Bedrock. Functionally, everything else works the same as before.

Addresses #141

[philikai]

Supportive of this PR, as it solves a big problem with the limits.

[pcgeek86]

I would love to see this PR merged, so we can use Amazon Bedrock with this tool. I haven't tried the tool yet, but will probably take a look with Tavily soon, since they have a [limited] free tier.

However, I could use the tool a lot more if it supported Bedrock APIs, since my company (AWS Premiere Partner) has a broad AWS deployment and customer base.

[mattbarlow-sg]

This has gotten a bit more complicated now that prompt caching is enabled in claude-engineer, which is not supported in Bedrock. The client has changed from client.messages to client.beta.prompt_caching.messages, and the system body has changed from a string to an array example.

Lastly, the response format differs, as cache attributes like this one will not exist in the Bedrock response.

I've been testing out workarounds to these issues in my fork, but it may be better to wait until prompt caching is available in Bedrock, so that the changes can be more minimal.