Export Content API does not have the option to export Rich Text Elements as plain text

[BryanValverdeU]

Describe the bug
Rich text elements are lost when exporting content as plain text

To Reproduce
Steps to reproduce the behavior:

1. Go to demo site
2. Create a table or a list
3. Export the content as plain text

Expected behavior
The exported content should contain a plain text representation of the rich text elements or allow the exportContent API to allow extensability to support how the rich text elements should be represented in Plain text

Screenshots
Content to be exported:

Result:

Expectation:

1. 123123
2. 123213
3. 213213
...

Additional context
Current implementation should not change, but should be extendable to support this.

[romanisa]

Encouraged open-source contribution from the AddIns team within Microsoft, where this ask came from.