Display relevant text message when user selects a single resource while managing a channel

[kmrinal19]

Summary

Fixes #7626 by displaying "Resource selected" message in place on "All resources selected" message when user selects a single resource while managing a channel.

Before:

After:

References

Fixes #7626

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Contributor Checklist

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Testing:

• Contributor has fully tested the PR manually
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Reviewer Checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[jonboiser]

Looks good, thanks!