[8.19](backport #45107) mod: update elastic/mito to version v1.21.0

[mergify]

Proposed commit message

mod: update elastic/mito to version v1.21.0

This adds support for:
* custom authentication headers
* AWS v4 request signing helpers

And upgrades the CEL runtime and compiler to v0.25.0.

Checklist

• 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.

Disruptive User Impact

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Closes [Filebeat] cel - support AWS request signing #40762

Use cases

Screenshots

Logs

---

This is an automatic backport of pull request #45107 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of c15a753 has failed:

On branch mergify/bp/8.19/pr-45107
Your branch is up to date with 'origin/8.19'.

You are currently cherry-picking commit c15a753f7.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   CHANGELOG.next.asciidoc
	modified:   x-pack/filebeat/input/cel/input.go
	modified:   x-pack/filebeat/input/cel/input_test.go

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   NOTICE.txt
	deleted by us:   docs/reference/filebeat/filebeat-input-cel.md
	both modified:   go.mod
	both modified:   go.sum

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[elasticmachine]

Pinging @elastic/security-service-integrations (Team:Security-Service Integrations)

[vishaangelova]

LGTM from a docs perspective