[DEV-4855] Add variant datamodel

[kgreav]

WARNING DO NOT MERGE WITHOUT CHANGING VERSION IN POM

Adds messages and RPCs required for variants.

Associated tasks

ewb-grpc
ewb-sdk-jvm
commons
ewb-network-routes
energy-workbench-server
power-factory-exporter
powerfactory-model-service
temporal-platform-definitions
temporal-platform-worker
evolve-app-server
opendss-model-processor
hosting-capacity-service

Test Steps

Explain in detail how your reviewer can test the changes proposed in this PR. If it cannot be tested, leave an explanation on why.

Checklist

If any of these are not applicable, strikethrough the line ~like this~. Do not delete it!. Let the reviewer decide if you should have done it.

Code

• I have performed a self review of my own code (including checking issues raised when creating the PR).
• I have added/updated unit tests for these changes, and if not I have explained why they are not necessary.
• I have commented my code in any hard-to-understand or hacky areas.
• I have handled all new warnings generated by the compiler or IDE.
• I have rebased onto the target branch (usually main).

Security

When developing applications, use following guidelines for information security considerations:

• Access to applications should be protected with security keys/tokens or usernames and passwords;
• All sessions are encrypted if possible;
• All application input is sanitised before being acted on (ie SQL statements, etc);
• Log messages, and especially client-facing ones, must be handled securely and must not leak credentials information (internal URLs, passwords, tokens).

• I have considered if this change impacts information security and made sure those impacts are handled.

Documentation

• I have updated the changelog.
• I have updated any documentation required for these changes.

Breaking Changes

• I have considered if this is a breaking change and will communicate it with other team members by posting it on the Slack breaking-changes channel.

surprisingly not breaking

[ryanjcoleman]

Task linked: DEV-4855 Update ewb-grpc