Update release process to include a rc and testing of upgrade deployment repo prior to release.

[marrobi]

Description

Build upon https://microsoft.github.io/AzureTRE/latest/tre-developers/release/

To ensure deployments and upgrades are smooth after a release, I suggest we create a release candidate first, ensuring extended tests complete on the release PR. Create a branch in the deployment repo with any updates. Test that on a fresh deployment and upgrade from the prior version. Once successful, verify docs are correct as far as secrets etc, create a release (not rc), and PR the new deployment branch.

consider before making a release

• Remove any Terraform or Database migrations that are from previous versions.
• Do an upgrade test from the last version, and not skipped any versions.
• Update terraform providers to latest versions