[DEV-6652] allow leaving allocation_limit_per_year unspecified

[Lax125]

Description

See title. This is done to avoid confusion in cases where the option is unused e.g. phase rebalancing.

Associated tasks

Tasks blocking this one:

• https://github.com/zepben/evolve-app-server/pull/303

Test Steps

Run intervention work package with allocation_limit_per_year unspecified. It should default to whatever EAS decides (should be 1 million)

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. (docs about running intervention completely missing. could update the examples instead)

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.

EAS must be upgraded to support null for allocationLimitPerYear

[ryanjcoleman]

Task linked: DEV-6652 Use defaults in eas client python

[AlexV-ZB]

I don't pretend to understand the exact code changes, but if it passed testing then I'm happy to deploy it