Post notification API and API versioning

[MeirShpilraien]

The PR is a proposal for API versioning using feature flags.
The PR introduce 4 new feature flags:

• min-redis-compatibility-version-7-2
• min-redis-compatibility-version-7-0
• min-redis-compatibility-version-6-2
• min-redis-compatibility-version-6-0 - default

User should set one of those feature flag which will indicate the minimum Redis version he want to be compatible with. Base on this, redismodule-rs will decide which API can be used and will manipulate existing API so it can be used conditionally.

For example, take the following API:

pub fn add_post_notification_job<F: Fn(&Context)>(self, callback: F)

This API require Redis version 7.2, so if min-redis-compatibility-version-7-2 feature is set the API is exposed as is. But if some other min-redis-compatibility-version-* is set, the API is changed to return APIResult which will allow to conditionally use this API if exists on the current Redis instance.

The PR also adds support for post notifications jobs and demonstrate how to use the new min-redis-compatibility-version-* flags.

Depends on: #302

[iddm]

Great job! 👍

[iddm]

So with this change, we should split the macros into two parts: internal and external. External is for the event handlers and other stuff for a user module, and internal is the stuff which only the redismodule-rs requires. I have already done that in my fork; please check it out: https://github.com/vityafx/redismodule-rs/tree/crate-refactoring-and-macros

[MeirShpilraien]

So with this change, we should split the macros into two parts: internal and external. External is for the event handlers and other stuff for a user module, and internal is the stuff which only the redismodule-rs requires. I have already done that in my fork; please check it out: https://github.com/vityafx/redismodule-rs/tree/crate-refactoring-and-macros

Yes I agree it makes sense to split it.

[MeirShpilraien]

@vityafx I think I addressed all the comments other then the naming which I commented on. Let me know what you think.