Update welcome-to-serverless.asciidoc

[JohannesMahne]

Format changes to the bullet points for the benefits of serverless.

[github-actions]

It looks like this PR modifies one or more .asciidoc files. These files are being migrated to Markdown, and any changes merged now will be lost. See the migration guide for details.

[eedugon]

@bmorelli25 : does it still make sense to apply changes in the serverless asciidoc documentation? This PR solves a small issue there.

Taking a look at the migrated documents it looks we have already fixed it in markdown :) https://docs-v3-preview.elastic.dev/elastic/docs-content/tree/main/deploy-manage/deploy/elastic-cloud/serverless

Should we cancel this PR or is it worthy to apply the fix in the current serverless docs too?

[bmorelli25]

Should we cancel this PR or is it worthy to apply the fix in the current serverless docs too?

We should apply this change, but not to the main branch. The serverless docs from now until 9.0 releases are being built from the do-not-delete_legacy-docs branch. I've changed the base branch of this PR to that branch. We can now merge this change and have the update go live today.