feat: Serialization version 2 deprecation notice

[jyejare]

What this PR does / why we need it:

• Shows deprecation warning for usage of Entity serialization less than version 2
• A util for re-serialization of entity ver 2 to ver 3
• A guide for reserializing the entity keys in an offline/online store
• A test case ensuring successful re-serilization of entity key

Which issue(s) this PR fixes:

Not fully but in the next release the serialization 2 would be completely deprecated to resolve #5180

Misc

[HaoXuAI]

This is nice but needs to be declared more explicitly. Can you update the all docs/Readme that has entity_key_serialization_version=2 to 3?

[ntkathole]

Please update the templates as well https://github.com/feast-dev/feast/blob/master/sdk/python/feast/templates/gcp/feature_repo/feature_store.yaml#L25

[jyejare]

@HaoXuAI @ntkathole This PR is just a notice of deprecation in the current release and helper function for users, that would help users to move to serialization version 3.

In next release, we will complete deprecating version 2 and below and stick to version 3. That time I will resolve your current queries @HaoXuAI @ntkathole :)

[HaoXuAI]

@HaoXuAI @ntkathole This PR is just a notice of deprecation in the current release and helper function for users, that would help users to move to serialization version 3.

In next release, we will complete deprecating version 2 and below and stick to version 3. That time I will resolve your current queries @HaoXuAI @ntkathole :)

sounds good!

[HaoXuAI]

LGTM!

[franciscojavierarceo]

not

Suggested change

	"The serialization version 2 and below would be deprecated in the next release. "
	"The serialization version 2 and below will be deprecated in the next release. "

[joyneuberger]

If I've updated my entity_key_serialization_version, can't I just run feast apply again rather than using the utility function to reserialize?

[jyejare]

@joyneuberger :
IF the data is stored/pushed in stores (offline/online) with version 2,
AND IF you are attempting to read the features from stores with version 3,
THEN you will have conflicts casue desearilization of version 2 entities wont be possible with version 3.
HENCE Reserializing it the perfect TODO here.

BUT IF You have not yet pushed data to the stores,
AND IF you have changed the version to 3,
THEN you are free to run feast apply

Most important thing here is the feast apply does not uses entity_key_serialization_version in any means. Why ?

1. Basicaly feast apply is only suppose to create infra(like tables, schema etc) for storing the data in stores, and it does not writes the actual data to the stores.
2. The entity key serialization version is used during runtime operations, not during the apply procedure, like:
   Online Feature Retrieval: When calling get_online_features(), the version is used to serialize entity keys for lookups in the online store.
   Online Feature Writing: When writing features to the online store (during materialization or push operations), the version determines how entity keys are serialized.
   Document Retrieval: For vector-based feature stores, the version affects how entity keys are serialized for similarity searches.

Finally,

• If you are concerned about data in stores that is already pushed, please use reserialize function.
• Else if you are concern about infra and the data is not already pushed to the stores, you can easily run feast apply.

Hope that answers !!