[Data AutoComplete] Allow case insensitve prefix auto complete value suggestions

[shahzad31]

Summary

As much as i love autocomplete service, it doesn't work where term data is case capital.

For example user_agent.name , where all values are capital case.

So if user types c to look out for Chrome, it will never appear in filtered out results.

This Pr adds a case insensitive first letter prefix in the terms include regex patter.

for example if user search for chrome, it will add include: '(chrome|Chrome).*'

and if user search for 'Edge' it will add '(Edge|edge).*'`

This will considerably improve user experience for autocomplete api.

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 2bd2d98
• Storybooks Preview

Metrics [docs]

✅ unchanged

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

cc @shahzad31

[lizozom]

@shahzad31 see #92783