[Cloudnative] Update null checks and if checks in the rename processor

[ishleenk17]

• Bug

What does this PR do?

This PR adds the if check for event.original and the ignore_missing check for the renaming of message to event.original
The packages where the changes are made are as below:

• istio
• nats
• nginx_ingress_controller
• stan

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.

Testing

After adding the check if event.original is null, it takes value of message as shown below:

If event.original is present. For testing it was set in the pipeline itself as below:

As a result the event.original has the original value and not the message value.

Related issues

• Relates Add checks to rename processor for the message field for all Observability Integrations #7822

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Build stats

• Start Time: 2023-09-25T11:39:30.158+0000

• Duration: 31 min 6 sec

Test stats 🧪

Test	Results
Failed	0
Passed	123
Skipped	2
Total	125

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (5/5)	💚
Files	100.0% (7/7)	💚
Classes	100.0% (7/7)	💚
Methods	95.192% (99/104)	👍 3.526
Lines	95.818% (1054/1100)	👎 -4.182
Conditionals	100.0% (0/0)	💚

[gizas]

I would expect some test evidence like a grok test or sth that this change worked. Apart from that is ok.

[ishleenk17]

I would expect some test evidence like a grok test or sth that this change worked. Apart from that is ok.

I have added the testing to the PR description.

[elasticmachine]

Package istio - 0.4.2 containing this change is available at https://epr.elastic.co/search?package=istio

[elasticmachine]

Package nats - 1.3.2 containing this change is available at https://epr.elastic.co/search?package=nats

[elasticmachine]

Package nginx_ingress_controller - 1.7.3 containing this change is available at https://epr.elastic.co/search?package=nginx_ingress_controller

[elasticmachine]

Package stan - 1.3.2 containing this change is available at https://epr.elastic.co/search?package=stan