Replace "Timeline" wording with "Activity" in order to be consistent with equivalent contexts throughout Nextcloud

[Jerome-Herbinet]

Replace "Timeline" with "Activity" in order to be consistent with other similar UI/UX contexts in Nextcloud (e.g. Files). Also, if you check the app description, the notion is "Activity" and not "Timeline" (description is relevant and is consistent with the "Activity" context).

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Documentation (manuals or wiki) has been updated or is not required

[Jerome-Herbinet]

Tried to make "npm run build", but doesn't produce any file to be committed. Not necessary in this case ?

[cypress]

Passing run #1461 ↗︎

0	17	0	0	0
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Details:

Merge 97b0eb6 into e8dd287...
Project: Deck	Commit: 1ccdb48ab8 ℹ️
Status: Passed	Duration: 03:03 💡
Started: Sep 26, 2023 12:36 PM	Ended: Sep 26, 2023 12:39 PM

_{This comment has been generated by cypress-bot as a result of this project's GitHub integration settings.}

[nickvergessen]

Fine by me

[github-actions]

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