[Console Monaco Migration] Fix variable replacement

[ElenaStoeva]

Fixes #185999

Summary

This PR fixes the variable replacement when the variable contains an object value .

How to test:

1. Go to Console and create the following variables:
   var1: {"match_all": {}}
var2: index
var3: match_all
2. Test using an object variable inside the request data:

GET _search
{
  "query": "${var1}"
}

should be sent as query: {match_all: {}} in the payload.
3. Test using a variable in the URL:
PUT /test-${var2} should be sent as PUT /test-index in the payload.
4. Test using a string variable in the request data:

GET _search
{
  "query": {
    "${var3}": {}
  }
}

should be sent as query: {match_all: {}} in the payload.
5. Test using undefined variables:

GET _search
{
  "query": {
    "${var4}": {}
  }
}

or PUT /test-${var5}
Both should be sent as they are.

[elasticmachine]

Pinging @elastic/kibana-management (Team:Kibana Management)

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: c0e1958

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
console	457.2KB	457.3KB	+99.0B

History

• 💔 Build #223463 failed 0242574
• 💔 Build #223428 failed af54a06

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @ElenaStoeva

[yuliacech]

Thanks a lot for fixing this bug, @ElenaStoeva! Verified locally