[3006.x] Fix find_json to not rely on newline after valid JSON

[m-czernek]

What does this PR do?

In this PR, we enhance the find_json function to work with valid JSONs that contain garbage right after the JSON end. This is a problem when the text contains JSON and, for example, deprecation messages, such as:

{
    "local": {
        "saltutil_|-sync_states_|-sync_states_|-sync_states": {
            "name": "sync_states",
            "changes": {},
            "result": true,
            "comment": "No updates to sync",
            "__sls__": "util.syncstates",
            "__run_num__": 0,
            "start_time": "14:35:37.150819",
            "duration": 1256.999,
            "__id__": "sync_states"
        },
...JSON continues...
}/usr/lib/python3.6/site-packages/salt/states/x509.py:214: DeprecationWarning: The x509 modules are deprecated. Please migrate to the replacement modules (x509_v2). They are the default from Salt 3008 (Argon) onwards.
  "The x509 modules are deprecated. Please migrate to the replacement "

Previous Behavior

Previously, if the JSON contains text right after the closing parenthesis, we either get a ValueError, or we get a wrong return (in the example above, the return value is "The x509 modules are deprecated. Please migrate to the replacement "

New Behavior

The find_json method is able to filter the text right after the closing parenthesis, and returns the valid JSON.

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

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[twangboy]

Please add a changelog for this

[m-czernek]

Thank you for taking a look @twangboy , chlog added.

[twangboy]

Once the testing pipeline is fixed you'll need to rebase this so the tests can run. Until then there's a pre-commit error. Looksl like you need to add .md to the changelog.