Help popup improvements

## Bug Description

1. Every help popup created by `gitlab.nvim` also shows the line: `✎ = draft; 󰌸 = unlinked comment; ✓ = resolved`. This should only be shown when the help is opened from the discussion tree. This can be easily fixed by adding a parameter the the `help.open()` function, so it could be a good first issue.
2. Every help on a `gitlab.nvim` popup contains the same information: `ZA: Perform linewise action`, `ZZ: Perform action`. This is not very helpful as the actions can be very different depending on the given popup/field. This information can be found in the plugin's help page, but a more informative info in the help popup would certainly be useful. This would require more work on the [set_popup_keymaps](https://github.com/harrisoncramer/gitlab.nvim/blob/a893f61bfc496e2468bdb1f9cc674e1b5c2e542b/lua/gitlab/popup.lua#L74) function.