Add codeowners for gcs, azureblobstorage inputs

[ebeahan]

Adding elastic/security-external-integrations as the explicit owner for gcs and azureblobstorage inputs.

[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 @ebeahan? 🙏.
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

[ShourieG]

LGTM

[elasticmachine]

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• Start Time: 2023-04-10T17:55:31.614+0000

• Duration: 13 min 35 sec

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