Host Logging for EOL or soon-to-be EOL .NET apps

#### What problem would the feature you're requesting solve? Please describe.
Show regular warnings when an EOL or soon-to-be EOL version is detected for a .NET app. This warning should be visible and accessible through App Insights.

#### Describe the solution you'd like
| Action | Condition | Behavior | Warning message. |
|-----------------|----------------|----------------|----------------|
| Upon app start/load | Functions version and/or stack version is out of support | Show warning message. | "Upgrade to Functions/Stack version as has reached end-of-life on and is no longer supported. Learn more: aka.ms/FunctionsStackUpgrade" |
| Regular cadence (24h?) | Functions version and/or stack version will be out of support in less than 6 months | Show warning message. | "Use Functions/Stack version as will reach end-of-life on and will no longer be supported. Learn more: aka.ms/FunctionsStackUpgrade" |

#### Describe alternatives you've considered
Warnings already exist for such apps in the portal and client tools, but host logging is critical for customer awareness.

#### Additional context
**Current Behavior:**
No warning/error is written by Host for EOL apps, and hence these logs are not available on AppInsights.

**Acceptance Criteria:**
Work item can be marked 'Completed' when we have implemented, tested and deployed the logic to show the above mentioned warning message when an app loads, and at a regular cadence thereafter when a Function App is configured with a stack runtime version that has a) reached its end-of-life date, or b) will reach its end-of-life date in <6months.

Additional information:

1. Getting current stack version information: [See this](https://github.com/Azure/azure-cli/blob/db09a85aba76aa31b791dc775b29f8e246461b30/src/azure-cli/azure/cli/command_modules/appservice/custom.py#L8270-L8327)

For Linux:
> All stacks - get app runtime version from linux_fx_version (from site config)

For Windows:
> Node: WEBSITE_NODE_DEFAULT_VERSION (from app setting)
> .NET: netFrameworkVersion (from site config)
> Java: javaVersion (from site config)
>PowerShell: powerShellVersion (from site config)

2. Compare against EOL dates in StacksAPI: [See this](https://github.com/Azure/azure-functions-ux/tree/dev/server/src/stacks/2020-10-01/stacks/function-app-stacks)

Start by tracing where the Functions host reads the runtime version from site configuration and app settings, using the linked Azure CLI stack-version logic as a reference. Compare the detected version with EOL dates from the linked StacksAPI data, then identify the host startup and recurring logging paths. Done means tested warnings appear on load and at the requested cadence for both already-EOL and soon-to-be-EOL runtimes, with messages visible to Application Insights.

Written by the indexing model from the issue text.