feat(aws): add https support

[andydunstall]

Adds HTTPS support to the AWS S3 client. (Will also add a dragonfly option to disable/enable HTTPS)

This uses the existing TLS client context and setup (since the AWS HTTP client writes directly to the socket, using TlsClient itself would be a pain so it just copies what it needs).

Since the HTTPS client is shared by multiple proactors, this still doesn't do connection caching. This has a bigger overhead with HTTPS than HTTP though is still negligible compared to the 8MB chunk uploads and downloads so I don't think thats an issue (users can disable HTTPS for S3 endpoints if preferred).

(Will add connection caching if/when replacing the AWS SDK and add a separate HTTP client per proactor rather than a global shared client)

TLS Not all AWS endpoints support TLS 1.3, though all support TLS 1.2, therefore updates the SSL context min version to 1.2 (down from 1.3)

• Testing locally the S3 endpoints don't support 1.3
• See https://aws.amazon.com/blogs/security/faster-aws-cloud-connections-with-tls-1-3/: "Over 65% of AWS service API endpoints now support TLS version 1.3. We are continuing work to enable TLS version 1.3 on AWS service API endpoints globally."

[romange]

You probably told me this but I do not remember now. Are we creating a connection for each request and then we close it?

[andydunstall]

Are we creating a connection for each request and then we close it?

Yeah - not great but given the HTTP client is accessed by multiple proactors seemed like its easiest just to keep it stateless (we don't have much control over access given the AWS SDK has a global static HTTP client - can improve later when removing the SDK)

Given each S3 operation is an 8MB upload/download the connection overhead is minimal (I ran tests using s3_demo using a single connection vs a connection per request and there wasn't much difference)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (077a00d) 77.50% compared to head (d348ff3) 77.56%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #163 +/- ## ========================================== + Coverage 77.50% 77.56% +0.05% ========================================== Files 98 98 Lines 7197 7197 ========================================== + Hits 5578 5582 +4 + Misses 1619 1615 -4 ``` [see 2 files with indirect coverage changes](https://app.codecov.io/gh/romange/helio/pull/163/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Roman+Gershman)

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