Unable to set environment setting for Batch task when there are equal signs in the value such as a Sql Connection string

**Related command**
az batch task create

**Is your feature request related to a problem? Please describe.**
Unable to set environment setting that contains an equal sign. F

**Describe the solution you'd like**
We should be able to escape the equal sign in the value of an environment setting either with a slash ('\') or by wrapping the entire value in quotes

```
az batch task create --environment-setting ConnectionString="Server=tcp:servername,1433"
```

or

```
az batch task create --environment-setting ConnectionString=Server\=tcp:servername,1433
```

**Describe alternatives you've considered**

**Additional context**
If I attempt to set a connection string like such SqlConnection="Server=tcp:servername.database.windows.net,1433;Initial Catalog=sqldb-app-dev_simplesearch;Persist Security Info=False;MultipleActiveResultSets=False;Encrypt" this fails with error invalid environment_setting_format