Add 12 column layout option for all dashboards

[kkmagician]

What type of PR is this? (check all applicable)

• Feature

Description

Reasoning

For more than a year of using Redash in my company and for personal projects one thing perplexed me: why there are only 6 columns available for widgets to be placed on a dashboard. Looking at other solutions (Grafana, Metabase, Superset, Shiny) all of them have more columns in the layout (12+). The number 12 is a great setting for any dashboard: it divides by 2, 3, 4 and 6, whereas 6 has only the 2 and 3 options. The handiness of dividing the layout into 4 even columns is apparent when using Counter or any other "small" widgets. See examples in the screenshots section.

Overall, the feature allows for a more fluid developer and consumer experience, while not forcing anyone to adopt the feature and not breaking old dashboards.

Implementation

• The old 6-column layout is used by default;
• New "Use 12 columns layout" checkbox in the dashboard editor – it switches the grid options used for the dashboard and updates the dashboard in the database: column dashboards.use_12_column layout (bool);
• When the checkbox is checked, background CSS grid changes accordingly;
• When the checkbox is unchecked, react-grid automatically smooshes all the widgets of width 7+.

Mobile & Desktop Screenshots/Recordings (if there are UI changes)

[arikfr]

I'm not sure why we picked 6 originally. But @gabrieldutra already started working on increasing number of columns in #4395. Our priorities shifted a bit, so it was left in draft. But I think we can switch to a single layout option (of 12 columns) with proper migration.

We should also look into decreasing the steps on the vertical axis.

[guidopetri]

@kkmagician , thanks for the PR! We've updated a lot of things now that we're Community-driven so - if you're still interested in getting this merged - would you mind rebasing off master to re-run the CI?

We're trying to clean up our PR todo list, so if you're not interested, that's fine - we'll close the PR in about a week if we don't hear back. If you're interested in reopening the PR afterwards, we would also very much welcome that.