feat: add grid addon

[Mastersam07]

Add grid addon.

This addon draws a grid on the widgetbook canvas. Where there is a DeviceFrameAddon, the grid is drawn on the device frame.

Seems like a good approximation of #17. Fields added to specify horizontal and vertical grid spacing.

Usage

To use grid on device, the DeviceFrameAddon must come before GridAddon in the addons hierarchy.

addons: [
        DeviceFrameAddon(devices: Devices.ios.all),
        GridAddon(),
      ],

List of issues which are fixed by the PR

#17

Screenrecord

Grid on widgetbook canvas

grid.mp4

Grid on device frame

device_grid.mp4

Checklist

• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making].
• All existing and new tests are passing.

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[Mastersam07]

Hi @YoussefRaafatNasry can you please take a look/review? This depends partly on #942

[YoussefRaafatNasry]

With the changes requested, we can detach this PR from the int knob PR, so we can merge each once separately.

Let me know what you think about the proposed changes and if you have any better ideas to improve this.

[Mastersam07]

@YoussefRaafatNasry changes made accordingly.

[Mastersam07]

@YoussefRaafatNasry changes made.

[YoussefRaafatNasry]

Great job @Mastersam07! Keep it up with the awesome PRs 💙

There will be some trivial changes (style, rewording in docs/Changelog) that I will do before merging this. The reason I will be doing them instead of adding comments is because:

1. They are nit-picks that you should not bother with, and focus more on your other PRs.
2. We have a lot of Hacktoberfest activity going on, and I am trying to minimize the back and forth on PRs.

I would still advice that you have a look on them, and feel free to ask any question them if needed.

[Mastersam07]

Great job @Mastersam07! Keep it up with the awesome PRs 💙

There will be some trivial changes (style, rewording in docs/Changelog) that I will do before merging this. The reason I will be doing them instead of adding comments is because:

1. They are nit-picks that you should not bother with, and focus more on your other PRs.
2. We have a lot of Hacktoberfest activity going on, and I am trying to minimize the back and forth on PRs.

I would still advice that you have a look on them, and feel free to ask any question them if needed.

Alright. Went through the changes, pretty straightforward. No questions