Add props to player alias subscriptions

[tudddorrr]

Subscription props

• Introduce a PlayerAliasSubscriptionProp entity so player relationships can store arbitrary key/value metadata.
• Add the migration, snapshot update and entity registration needed to persist props.

API support

• Let clients pass props when creating a relationship, so metadata is set at subscription time.
• Add a PATCH endpoint to add, overwrite or delete props on an existing subscription, where a null value removes the prop.
• Limit prop updates to the subscription owner so a subscribed player can't modify the other side's props.

Validation & caching

• Apply the existing length and profanity rules to subscription props, rejecting the whole request and returning the offending props when any are invalid.
• Invalidate cached relationship responses whenever props change so subscribers and subscriptions always reflect the latest values.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.75%. Comparing base (a9406b4) to head (8a20ec1).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1091      +/-   ##
===========================================
+ Coverage    98.73%   98.75%   +0.02%     
===========================================
  Files          530      532       +2     
  Lines         8153     8206      +53     
  Branches      1059     1067       +8     
===========================================
+ Hits          8050     8104      +54     
  Misses          36       36              
+ Partials        67       66       -1     

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