Add support for region/zone for Vertex AI service in GCP module

[ishleenk17]

Checklist

• [ x ] 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
• [ x ] I have added tests that prove my fix is effective or that my feature works
• [ x ] I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Related issues

• Closes Support GCP region for Vertex AI #41360

Screenshots

Data coming in from all the regions

The config of GCP for aiplatform service with region enabled as us-east4

Data coming in after region filter is applied

Config with regions enabled

Data after the above Regions Filter

[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 @ishleenk17? 🙏.
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-8./d is the label to automatically backport to the 8./d branch. /d is the digit

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.

[muthu-mps]

LGTM!