Allow redisVersion to change, promoted some fields to GA

[modular-magician]

closes hashicorp/terraform-provider-google#9174
closes hashicorp/terraform-provider-google#8306

Allow redis_version to be updated.
Promoted transit_encryption_mode and server_ca_certs to GA

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• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
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• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
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• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

redis: allowed `redis_version` to be upgraded on `google_redis_instance`

redis: promoted fields `transit_encryption_mode` and `server_ca_certs` to GA on `google_redis_instance` (GA)

Derived from GoogleCloudPlatform/magic-modules#4838