Add keymaps for start, resume, submit and discard Reviews

Describe what this PR does / why we need it

The process of opening a pull-request and starting a review was a little disconnected, as we had keymaps to almost everything we can do with a pull-request, except for starting a review.

https://github.com/pwntester/octo.nvim/assets/4634613/68458e0b-d791-4ab4-b568-3ef8532142ac

Describe how you did it

I followed the project standard and created named mappings that mirror the configuration keys and added them to:

Pull request buffer (pull_reqest)
The diff-view of the Review (review_diff)
The review pane (file_pane)

The new commands are:

Command	Binding
`review_start`	`<leader>vs`
`review_resume`	`<leader>vr`
`submit_review`	`<leader>vs`
`discard_review`	`<leader>vd`

Describe how to verify it

Start and resume a PR:

Open a Pull-Request
press <leader>vs to start a review
press Ctrl+c to close the review
press <leader>vr to resume the review

Submit or discard a PR

Open a Pull-request
1. press <leader>vs to start a review
from the diff-view or the files pane, press <leader>vs to open the submit modal
Run the command :q to close it
press <leader>vd to discard the review, you should see a prompt asking to confirm.

Special notes for reviews

Aside from the keybindings, this PR also fixed the Ctrl+C to close the review, that wasn't working, as it wasn't passing the current tab as an argument to the close() function, so the key press was just ignored.

pwntester / octo.nvim