…o file (#1691)

## Why make this change?

- Closes #1687

## What is this change?

- Set the Encoder for JsonSerializationOptions to be
[`JavaScriptEncoder.UnsafeRelaxedJsonEscaping`](https://learn.microsoft.com/en-us/dotnet/api/system.text.encodings.web.javascriptencoder.unsaferelaxedjsonescaping?view=net-7.0)
instead of the default encoder.
- Although [this
article](https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/character-encoding#serialize-all-characters)
mentions use this encoder with caution, since we are sure the file
contents will be deserialized as UTF-8 JSON, we should be safe to use
this encoder.
- We were using this encoder previously from the fix in #1386, but with
#1402, that original fix was essentially not being used since #1402
introduced usage of the new `GetJsonSerializerOptions()` function in
`RuntimeConfigLoader`.

## How was this tested?

- [X] Unit Tests. `TestSpecialCharactersInConnectionString` is moved to
the `ConfigGeneratorTests` since keeping it as part of `InitTests` with
the Verify framework wasn't really testing the scenario since we ignore
connection strings in the snapshots.
- This regression from #1402 was not caught because this test scenario
was effectively being skipped.
- Note, this test is modified to explicitly compare the expected and
actual json string from file since any usage of
JsonSerializer/JObject.Parse would require using the same encoder to
deserialize making the test itself run similar code which it is testing.
Parsing into JSON objects would treat `\u0027` and `'` as equal whereas
string comparison wont. Hence, comparison using string is necessary to
catch regressions here.

## Sample Request(s)

BEFORE:
`dab init --host-mode development --database-type mssql
--connection-string "@env('my-connection-string')"`

creates the configuration file as follows:

```
{
  "$schema": "https://github.com/Azure/data-api-builder/releases/download/v0.8.49/dab.draft.schema.json",
  "data-source": {
    "database-type": "mssql",
    "connection-string": "@env(\u0027my-connection-string\u0027)",
    "options": {
      "set-session-context": false
    }
  }
```
Note, the value of connection string.

AFTER: Same command creates the following file:
```
{
  "$schema": "https://github.com/Azure/data-api-builder/releases/download/v0.8.49/dab.draft.schema.json",
  "data-source": {
    "database-type": "mssql",
    "connection-string": "@env('my-connection-string')",
    "options": {
      "set-session-context": false
    }
  }
```

---------

Co-authored-by: Abhishek Kumar <[email protected]>

- Cherry Picks #1691 into release/0.8

---------

Co-authored-by: Abhishek Kumar <[email protected]>