Support Hash-Based Routing

[hoffmaen]

This Pull-Request replaces #4696.

This Pull-Request adds support for hash-based routing to Cloud Controller.

Summary:
The routes model is enhanced as follows:

• hash is added as a valid loadbalancing option
• hash_header is added as a per-route option. The option is mandatory when loadbalancing=hash
• hash_balance is added as a per-route option. The option is optional when loadbalancing=hash

Validation of these options is added when creating and updating both via API and via manifest. All validations that do not need the context of a potentially existing route during an update, are executed in the message:

• Hash Balance must be numeric
• Hash Header and Hash Balance must not be specified together with round-robin or least-connection
• Values for Hash Header and Hash Balance must not be arbitrarily long

Further validations and cleanups are performed on the route model, as they need the context of existing routes:

• The route options from the update message are merged with existing routes, when existing
• When the loadbalancing algorithm is hash, then Hash Header must be specified
• When the loadbalancing algorithm is switched from hash to something else (or when it is removed), also Hash Header and Hash Balance options are removed
• Hash Balance is always stored as a string, and is always trimmed to a numeric value with one decimal place

The route options are still stored as a raw JSON string in the routes table.

Links:

• capi-release implementation issue
• routing-release Pull-Request for hash-based routing support
• RFC-0042

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