Max connections override

Added max connections override for capping the amount of active client connections.

Improving request flow

Request preparation (ie: signing, reading from a stream, etc.) will now happen in a different ELG from the network IO ELG.

User-Agent Changes

• Adding user-agent information about the client to request headers.

Bug Fixes

• Fixing bug with num_active_vip_connections counter
• Fixing two race conditions related to client clean up

Logging Changes

• Additional logging and removing toggle for client stats logging.

New managed thread API

Convert to new managed thread system for threads that cannot be reliably explicitly joined.

v0.1.6

• Addressed the issue of downloading an empty file

Streaming Requests Bug Fix

• Fix for issue where a canceled meta request could hold onto requests that are waiting to be streamed, preventing it from being cleaned up.

Various Improvements

• Refactoring meta request types to have a cleaner implementation/improve cancel functionality stability.
• Added a mitigation for issue where global request limit was being hit, which was negatively impacting performance.

Test updates and tls failure crash fix

• Fix a client creation crash when tls initialization fails
• Mark a few more tls-using tests as net