fixbug, Content-Type validate

[worker24h]

OkHttp，'; charset=utf-8' append to 'application/json' by self, for example

POST /api/v1/push HTTP/1.1
User-Agent: PostmanRuntime/7.29.2
Accept: */*
Accept-Encoding: gzip, deflate, br
Authorization: Basic AAAAAAAAAAAAADDDDDDDDD=
Content-Type: application/json; charset=UTF-8
Content-Length: 213
Host: abc-test-ok.aaa
Connection: keep-alive

but PostMan is not.
So, to be compatible with these two forms (application/json, application/json; charset=utf-8) to strings.Contains

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• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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[botelastic]

This pull request doesn't have a Team:<team> label.

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @worker24h? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit