WIP: Add RFC for export direction

[ptodev]

PR Description

This is a draft RFC which reevaluates whether we should enforce a specific direction for the exports of Flow components.

Please feel free to drop comments with any suggestions, for example:

• Additional pros and cons
• Additional examples
• Your own conclusion

Which issue(s) this PR fixes

Fixes grafana/alloy#470

Notes to the Reviewer

Most of the lines are very long. It's easiest to edit the markdown this way and have them wrap around in the editor. For the final draft I will make the lines shorter, as is the convention for MD files.

[rfratto]

I’m concerned we’re not touching enough on how it will be possible to reverse the direction of some components in a way which is easy to maintain and that isn’t prone to bugs.

[ptodev]

An additional interesting use case is the one described in grafana/agent#3939 and grafana/agent#3656

[ptodev]

Closing this since it's not a priority at the moment. It'll also likely need a whole new discussion if we're to consider it again.