[Files] Copy updates and file picker single select

[jloleysens]

Summary

• Several copy updates (for e.g., [Files] Filepicker #143111 (comment))
• Adds new flag to support selecting a single or multiple files

Checklist

Delete any items that are not applicable to this PR.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Unit or functional tests were updated or added to match the most common scenarios

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServicesUx)

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 4624d27
• Storybooks Preview

Failed CI Steps

• FTR Configs #23

Test Failures

• [job] [logs] FTR Configs #23 / dashboard drilldowns Dashboard to dashboard drilldown Create & use drilldowns test dashboard to dashboard drilldown browser back/forward navigation works after drilldown navigation

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
files	26.5KB	26.8KB	+214.0B

Unknown metric groups

API count

id	before	after	diff
files	275	276	+1

ESLint disabled in files

id	before	after	diff
osquery	1	2	+1

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	19	21	+2
fleet	57	63	+6
osquery	103	108	+5
securitySolution	439	445	+6
total			+19

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	20	22	+2
fleet	65	71	+6
osquery	104	110	+6
securitySolution	516	522	+6
total			+20

History

• 💔 Build #84605 failed 002ed19

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@elasticmachine merge upstream

[Dosant]

Tested single mode. works well 👍
thanks