Improve documentation on feast apply

[adchia]

Several users have expressed confusion on how feast apply works. Some examples:

• Why feast apply requires permissions
• What we mean by "validate features" on https://docs.feast.dev/reference/feast-cli-commands#apply
• What infrastructure is managed via feast apply (as referenced on https://docs.feast.dev/reference/feast-cli-commands#apply)
• What the impact is when users specify feature views with schema / event timestamp column inference (i.e. at the time of feast apply, it serializes a fully specified schema into the registry)
• What the impact is when users have feature services that depend on feature views that change

Some of this might be helped with feast plan work, but others should have better documentation

[adchia]

In the context of a GCP provider, I had given this as a Slack response:

1. Feast will not create tables within BigQuery
2. Feast will create tables in the online store however matching the schema of the feature view
3. Validation - Feast does very minimal validation. It checks for unique feature view / data source names. This applies more if you are relying on Feast to infer types or features or event timestamp columns from a data source

This is why the permissions require the ability to modify datastore (which is assumed to be the online store for a gcp provider unless you override) as well as read from BigQuery

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.