Unable to run "func durable..." commands when using hubName set in local.settings.json

### Description
When hubName in host.json is set to a string like `%TaskHubName%` commands run locally that start with "func durable" always return the following message:

Invalid container name. Check MSDN for more information about valid container naming.

### Expected behavior
The command to run normally, having retrieved the hubName value from the app settings.

### Actual behavior
The command does not run, and instead returns the error message `Invalid container name. Check MSDN for more information about valid container naming.`

### Relevant source code snippets
host.json:
```json
{
"version": "2.0",
"logging": {
"fileLoggingMode": "always",
"logLevel": {
"default": "Information"
}
},
"extensions": {
"durableTask": {
"hubName": "%TaskHubName%"
}
}
}
```

### Known workarounds
Using a "normal" value for `hubName`

```json
{
"version": "2.0",
"logging": {
"fileLoggingMode": "always",
"logLevel": {
"default": "Information"
}
},
"extensions": {
"durableTask": {
"hubName": "mylocalhubname"
}
}
}
```

### App Details

- **Durable Functions extension version (e.g. v1.8.3)**: v2.1.1
- **Azure Functions runtime version (1.0 or 2.0)**: 2.0
- **Programming language used**: C#

Reproduce the issue with hubName set to "%TaskHubName%" in host.json and the corresponding value in local.settings.json, then run the affected "func durable" commands. Compare this with a literal hubName and trace how the command retrieves the app setting. Done means the commands run normally with the substituted hubName instead of returning the invalid container name error.

Written by the indexing model from the issue text.