add iteration autocomplete to RTE

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What does this MR do and why?

This MR aims to add the iteration feature to the RTE.

References

It aims to fix the issue #407511

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Clone this git repo
2. Got to any page that has the RTE
3. enter *iteration: on the editor, and you should be able to see a list of autocomplete options for iterations