Add docs about how to migrate out from the array type

[jsoriano]

array type is going to be removed, see elastic/package-spec#408 and elastic/package-spec#412.

[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: 2022-09-12T15:11:41.459+0000

• Duration: 27 min 11 sec

Test stats 🧪

Test	Results
Failed	0
Passed	829
Skipped	0
Total	829

🤖 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% (34/34)	💚
Files	66.929% (85/127)	👍
Classes	61.667% (111/180)	👍
Methods	48.834% (356/729)	👍
Lines	32.231% (3225/10006)	👍
Conditionals	100.0% (0/0)	💚