[7.x] [APM] Align APM severity levels with ML (#77818)

[dgieselaar]

Backports the following commits to 7.x:

• [APM] Align APM severity levels with ML ([APM] Align APM severity levels with ML  #77818)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 2c8c2f4

Build metrics

@kbn/optimizer bundle module count

id	value	diff	baseline
apm	1257	+1	1256
ml	1408	+2	1406
total		+3

async chunks size

id	value	diff	baseline
apm	5.0MB	-2.6KB	5.0MB
ml	8.1MB	-23.0B	8.1MB
total		-2.6KB

page load bundle size

id	value	diff	baseline
apm	44.0KB	+1.7KB	42.3KB
ml	873.5KB	+1.2KB	872.3KB
total		+2.9KB

distributable file count

id	value	diff	baseline
default	47669	+1	47668

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream