[Post to relay] Update button to include relay selection menu

[setch-l]

This ticket contains multiple stories to allow users to select which relay their post goes out to:

Update text of the Post button

Given that I am user of Nos
When i open the editor
I should see Post to all my relays with a down arrow

Designs
https://www.figma.com/design/s0qf4VmyQygydP8MIQazZc/Nos?node-id=7560-7377&t=Yrzf5JecQ3xkgwZT-1

Clicking the left side of the post to all my relays

Given that I am a user of nos
When I click the left side of the Post to all my relays button
Then the note should post
Note the button is disabled until there is content available to post:
Designs:
https://www.figma.com/design/s0qf4VmyQygydP8MIQazZc/Nos?node-id=7560-7377&t=Yrzf5JecQ3xkgwZT-1

Clicking the down arrow on the Post to all my relays

Given that I am a user of Nos
When I click the down arrow (right side) of the Post to all my relays button
Then I should see a menu with all of my relays listed, a description of each, and All my relays toggled on by default

Toggling a relay to on

Given that I am a user of Nos viewing the relays posting menu
When I toggle another relay on
Then the All my relays toggles off

Users can toggle more than one relay to on.

Clicking outside the menu after selecting relays

Given that I am user of Nos
When I click outside the relay menu
Then it should close the button label should change to Post to # relays, where # is the count of relays.

Clicking post on # relays

Given that I am a user of Nos
When I click post and have selected something other than all my relays
Then the note should only be posted to the relays I’ve selected.

[lingoslinger]

@joshuatbrown I'd like to take this on if no one else minds. If that is cool please assign to me.
@setch-l I have one question - if a user first turns all my relays off, then selects all of their relays individually, I assume that the all my relays toggle should go back to on - please verify. Thanks!