[Streams] Update EditPolicyModal copies

[SoniaSanzV]

Part of #254852

Summary

From the analysis @mdbirnstiehl did:

For the title, how about "This update affects 6 streams and 4 indices"

For the managed policy warning, how about the following to maybe suggest saving as a new policy:

Modifying a managed policy
This policy is managed by Elasticsearch. Modifying it can cause unexpected behavior. To avoid unintended changes, save as a new policy instead.

For the body text:
7 streams and 5 indices use the ILM policy you're updating. To apply your changes to only this stream, save as a new policy.

For the CTA:

How about [Update current policy][Save as new policy]? Maybe these are too long and might not look quite right, but if they fit, I think this is more explicit.

How to test

View the component in Storybook:

yarn storybook streams_app

[elasticmachine]

Pinging @elastic/kibana-management (Team:Kibana Management)

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 60a8641

Failed CI Steps

• Jest Tests #11

Test Failures

• [job] [logs] Jest Tests #11 / ChangePasswordModal render disables submit button when passwords do not match
• [job] [logs] Jest Tests #11 / IncludeExcludeComponent should prevent identical include and exclude values when creating multiple options

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
streamsApp	1.8MB	1.8MB	+83.0B

cc @SoniaSanzV