switch to colon fences when content requiries it

[stevejpurves]

In some cases it is necessary to use colon fences instead of backticks when content itself contains backticks. An example is shown in this issue where there is a role within the first line of the list-table directive.

As stated in that issue - this is a documentation issue from a myst-cli point of view, however the curvenote cli maybe needs to have some additional logic to switch to colon fences when it writed markdown content during curvenote pull

[fwkoch]

For what it's worth, myst-to-md uses colon fences for directives that may have backticks in the args - if we are able to hookup curvenote pull to use that, this will be resolved. executablebooks/mystmd#303