Ruby SDK - Phase 1 - Initial Comment Period

[cretz]

⚠️ Next PR round opened at #93

Summary

• This is the proposal for the first phase of the Ruby SDK.
• See it rendered.
• Much of this is inspired by the current Temporal Ruby SDK (and its proposals which were moved to a sub directory) and our other SDKs.
• Use this PR for comments/discussion. Don't be afraid of making too many comments; if it gets too noisy, I'll just create another PR.
• Any points of contention will be discussed in-person by the SDK team and a decision will be made.

[cretz]

I have updated the proposal with the following:

• Clarify why we need typing at all
• Use Temporalio::SearchAttributes as both the collection and class under which all nested search attribute things reside
• Use Temporalio::Metric as both the base metric and class under which all nested metric things reside
• Clarified use of Options structs on client/connection
• Clarified there will be a CloudOperationsClient
• Made namespace a required field instead of defaulting to default
• Changed Temporalio::Converter module to Temporalio::Converters
• Changed Temporalio::Converters::PayloadConverter to be a simple base class instead of having it impl composite, and created Temporalio::Converters::PayloadConverter::Composite
• Updated activity lifecycle to say we will instantiate activities on each attempt if registered as a class, or we will just call method on existing instance if registered as an instance
• Clarified that activity executors can validate activities at registration time instead of runtime, which means that workers have to be created in an async context if they have any async-context-needed activities (as opposed to just run in an async context)

[cretz]

Closing this PR in favor of https://github.com/temporalio/proposals/pull/93 for a fresh round of comments. Will link back to this one for posterity, but unaware of any unresolved issues here. Anyone here can feel free to comment on https://github.com/temporalio/proposals/pull/93.