[o365] Preserve event.original from o365audit field

[chemamartinez]

Proposed commit message

When using the CEL input to collect logs from Microsoft Office 365, the CEL input format the read event into a field called o365audit. For that cases, event.original must be copied from this field instead of message which doesn't appear.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2023-11-06T19:25:35.041+0000

• Duration: 16 min 27 sec

Test stats 🧪

Test	Results
Failed	0
Passed	25
Skipped	0
Total	25

🤖 GitHub comments

Expand to view the GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (1/1)	💚
Files	100.0% (1/1)	💚
Classes	100.0% (1/1)	💚
Methods	100.0% (16/16)	💚
Lines	81.579% (744/912)	👎 -17.216
Conditionals	100.0% (0/0)	💚

[elasticmachine]

Package o365 - 1.26.0 containing this change is available at https://epr.elastic.co/search?package=o365