docs: separate custom query documentation into a new file

See merge request gitlab-org/gitlab-vscode-extension!228

feat: add "Merge requests I'm reviewing" custom query

See merge request gitlab-org/gitlab-vscode-extension!226

feat: only poll for new status bar information in focused window

See merge request gitlab-org/gitlab-vscode-extension!227

During the refactoring, we had to disable one test that hid the MR
status bar item when there wasn't any project. This commit fixes the
scenario by checking whether a GitLab project can be fetched for the
current workspace and if not, we hide all the status bar items. This
also happens to fix the #71.

The "init" keyword wasn't accurate anymore. We were simply creating the
StatusBarItems and it made more sense to inline the creating so the
reader instantly knows what's happening.

When there is no workspace folder, we will skip refreshing all together.
This scenario can occur when user didn't open a project, or they use
multi-root project and don't have a file open in the editor.

This commit changes the `refreshPipelineAndMr` method to refresh all
status bar items. Instead of using the class properties to communicate
between methods, we are passing values to the `updateMrItem` and
`fetchMrClosingIssue`. This makes the code easier to reason about
because there is fewer side-effects

This was a great win. We already had to fetch the MR anyway in the
`refreshPipeline` method, this commit reduces the `fetchBranchMR` method
to a simple presentation layer, saving us one or more API calls.

We separate methods for fetching the MR and closing issue so we can
later significantly reduce the MR fetching method.

This is best demonstrated by the following snippet from this commit:

```diff
- this.fetchBranchMrAndClosingIssue();
+ await this.fetchBranchMR();
+ await this.fetchMRIssues();
```

Instead of registering a new command, which was basically a callback, we
can declare what the item is supposed to do instead, reducing the amount
of procedural code.

Instead of triggering always one command which will decide what to do,
we can decide what to do at the time when we change the status bar item.

Instead of registering a new command, which was basically a callback, we
can declare what the item is supposed to do instead, reducing the amount
of procedural code.

Instead of triggering always one command which will decide what to do,
we can decide what to do at the time when we change the status bar item.

The current order is:
1. Pipeline
2. Closing issue
3. MR

But logically it must be a different order:

1. Pipeline - pipeline is the most common out of the three
2. MR - some branches have an MR
3. Closing issue - can only exist if there is an open MR

fix: when fetching pipeline jobs fails, only log error, no notification

See merge request gitlab-org/gitlab-vscode-extension!225

docs: introduce minimum supported version

See merge request gitlab-org/gitlab-vscode-extension!221

refactor: convert status_bar to TypeScript

See merge request gitlab-org/gitlab-vscode-extension!224

fix: ci variables links are broken

See merge request gitlab-org/gitlab-vscode-extension!215

We introduced `asMock` helper that prevents us from having to always
type cast the mock with `as jest.Mock`.

We changed imports and exports to ES modules. We had to specify all
function input types and types of class properties. We added many
non-null assertions to make the type checker pass.

We changed GitLabJob to RestJob to match the naming convention and used
it in the status_bar.

We exit the openers early if there is no workspaceFolder. On top of
that, we added one assertion for the project API response being present.

Use export keyword instead of specifying all the exports at the end of
file (CommonJS)

Change imports to ES modules, specify function input types and add
non-null assertions (! at the end of the expression) to make the type
checker pass.

feat: respond to an MR diff thread

See merge request gitlab-org/gitlab-vscode-extension!222

feat(mr review): show change type for each changed file

See merge request gitlab-org/gitlab-vscode-extension!213