ampersand sign converted into unicode when added to analytics config.

**Bug Description**

A user reported on support forums that the `&` is being converted to Unicode character `\u0026` when being added to the analytics config.

After disabling optimizer it did output correctly
`add_filter( 'amp_enable_optimizer', '__return_false' );`

**Steps to reproduce**
You can reproduce using the AMP plugin for WordPress, steps assuming that you have WordPress site with AMP plugin installed

Step 1 : Login as Admin
Step 2: Goto AMP->Settings->Analytics
Step 3: Enter the type as "test" (you can add anything as type was unknow from support topics)
Step 4: add JSON config as below

```json
{
"requests": {
"custom_params": "cp1=test&cp2=test"
},
"vars": {
"env": "-preproduction"
},
"triggers": {
"trackConsent": {
"on": "visible",
"request": "impression"
}
}
}
```

**Expected Output**
Same output as entered in config.

**Current Behaviour**

```json
{
"requests": {
"custom_params": "cp1=test\u0026cp2=test"
},
"vars": {
"env": "-preproduction"
},
"triggers": {
"trackConsent": {
"on": "visible",
"request": "impression"
}
}
}
```

**Screenshot**
| Input | Output |
| ------------- | ------------- |
|  |  |

Reproduce the analytics configuration steps with the AMP optimizer enabled, then trace how the JSON config is processed and emitted. Confirm the fix by checking that the ampersand in custom_params remains unchanged in the generated output.

Written by the indexing model from the issue text.