Flex Consumption SKU for Placeholder

#### What problem would the feature you're requesting solve? Please describe.
We will have three different scenarios for Linux Consumption hosts:
1. Consumption V1 running on Atlas
2. Consumption V1 running on Legion (new)
3. Flex Consumption running on Legion

We can differentiate between scenarios **1 vs 2** and **1 vs 3** based on the platform it's running on (IsLinuxConsumptionOnAtlas() and IsLinuxConsumptionOnLegion())
We will need a way to differentiate between scenarios **2 vs 3** for when we migrate cv1 onto Legion.
The **_WEBSITE_SKU_** can only be referenced for specialized hosts, and the environment will be the same for consumption v1 and flex consumption because both will be running on Legion.

#### Describe the solution you'd like
FunctionsPodSerivce injects **_WEBSITE_SKU_NAME_** for Flex Consumption pods which will allow us to determine the sku of the host even when in placeholder mode ([code](https://msazure.visualstudio.com/One/_git/AAPT-Antares-Websites?path=/src/Hosting/Functions/FunctionsPodService/PodBuilder/FunctionsWorkerPodBuilderStrategy.cs&version=GBdev&line=60&lineEnd=61&lineStartColumn=1&lineEndColumn=1&lineStyle=plain&_a=contents)). 
For the 1st and 2nd scenarios, **_WEBSITE_SKU_NAME_** will not be set (no new changes)
For the 3rd scenario, **_WEBSITE_SKU_NAME_** will be set to _FlexConsumption_ [PR](https://msazure.visualstudio.com/One/_git/AAPT-Antares-Websites/pullrequest/8991851)

#### Describe alternatives you've considered
Thought about just using the existing **_WEBSITE_SKU_** but this could result in unexpected changes

#### Additional context
Add any other context or screenshots about the feature request here.

The issue points to FunctionsWorkerPodBuilderStrategy.cs in the external AAPT-Antares-Websites repository and PR 8991851; start there, then trace how the host consumes WEBSITE_SKU_NAME. Done means Flex Consumption can be distinguished from Consumption V1 on Legion while Atlas and existing scenarios retain their current behavior.

Written by the indexing model from the issue text.