[API] Clarify which endpoints return committed / pending transactions

[banool]

Description

In this PR I make it clearer which endpoints return transactions in which states.

I also remove a todo about /encode_submission. We shouldn't be encouraging people to use this endpoint, it is insecure.

Test Plan

👀

---

This change is 

[banool]

@clay-aptos feel free to take over from here if you want to make some changes!

[clay-aptos]

@clay-aptos feel free to take over from here if you want to make some changes!

Thanks, @banool ! I made some small edits directly in a commit here.

[banool]

Thanks, I'll make the changes to the code and regenerate accordingly.

[clay-aptos]

Thanks, I'll make the changes to the code and regenerate accordingly.

Here is the replacement: https://github.com/aptos-labs/aptos-core/pull/5376