Add StringAsset support to CopyToRemote

[MunemHashmi]

Summary

• Allow CopyToRemote to accept `StringAsset` (text content) in addition to `FileAsset` and `FileArchive`
• Enables copying generated content like config files, certificates, or scripts directly to remote hosts

Changes

• Modified `Check()` to allowAdd StringAsset support to CopyToRemote text-based assets
• Added `copyTextContent()` function for SFTP text transfer
• Added helper methods and tests
• Updated documentation

Fixes #825

[github-actions]

PR is now waiting for a maintainer to run the acceptance tests.
Note for the maintainer: To run the acceptance tests, please comment /run-acceptance-tests on the PR

[guineveresaenger]

Hi @MunemHashmi - thank you so much for this pull request. Apologies for the delay in getting back to you - we must have missed this due to the holidays.

Before we consider your changes, could you please do the following?

1. rebase (it's a renamed function and safer file permissions)
2. run make build to generate the schema and provider SDKs and commit the resulting changes.

Please let us know if you'd like help with either of the above. Thank you again!