topsite'size on dashboard should be customizable

[jlmxyz]

relate to
#353

Description

the widget is by far too small, user must be able to change it's size

Steps to Reproduce

1. open a new tab
2. try to resize by drag... not working
3. try to go in dashboard settings, in topsite, no option is given to enter a size
4. go in brave://flags, search dashboard, nothing appears

Actual result:

a ridiculous 2x6 icons set is displayed

Expected result:

I shall be able to fill the entire screen with my shortcuts

Reproduces how often:

100%

Brave version (brave://version info)

Brave	1.46.127 Chromium: 108.0.5359.48 (Official Build) unknown (64-bit) 
Revision	18ceeca0d99318e70c00d2e04d88aa55488b5c63-refs/branch-heads/5359@{#854}
OS	Linux
JavaScript	V8 10.8.168.20
User Agent	Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/108.0.0.0 Safari/537.36
Command Line	/usr/bin/brave-bin --disable-domain-reliability --enable-dom-distiller --component-updater=url-source=https://go-updater.brave.com/extensions --origin-trial-public-key=bYUKPJoPnCxeNvu72j4EmPuK7tr1PAC7SHh8ld9Mw3E=,fMS4mpO6buLQ/QMd+zJmxzty/VQ6B1EUZqoCU04zoRU= --sync-url=https://sync-v2.brave.com/v2 --lso-url=https://no-thanks.invalid --variations-server-url=https://variations.brave.com/seed --variations-insecure-server-url=https://variations.brave.com/seed --flag-switches-begin --enable-features=EnableDrDc --flag-switches-end
Executable Path	/opt/brave/brave
Profile Path	/home/jlm/.config/BraveSoftware/Brave-Browser/Profile 7