Add newline before `exports-last`

Hello, I will be glad if you consider adding a new feature to [import/exports-last](https://github.com/import-js/eslint-plugin-import/blob/HEAD/docs/rules/exports-last.md):

### Add option to [import/exports-last](https://github.com/import-js/eslint-plugin-import/blob/HEAD/docs/rules/exports-last.md), to enforce a specific number of newlines **before the first** `export` keyword.

Similarly to an option implemented in [import/newline-after-import](https://github.com/import-js/eslint-plugin-import/blob/HEAD/docs/rules/newline-after-import.md), I wish to have 2 blank lines before the **first** `export` section.

---

For example, when `count` is `2`:

#### Valid:
```js
import { groups } from '../../db';
import { errors } from '../../errors';

const getGroupById = (id)=> {
if (!Object.keys(groups).includes(id)) {
throw new errors.NotExistsError({
message: `The group id '${id}' not found`
});
}
return groups[id];
};

export { getGroupById };

```

#### Invalid:
```js
import { groups } from '../../db';
import { errors } from '../../errors';

const getGroupById = (id)=> {
if (!Object.keys(groups).includes(id)) {
throw new errors.NotExistsError({
message: `The group id '${id}' not found`
});
}
return groups[id];
};

export { getGroupById };

```
```js
import { groups } from '../../db';
import { errors } from '../../errors';

const getGroupById = (id)=> {
if (!Object.keys(groups).includes(id)) {
throw new errors.NotExistsError({
message: `The group id '${id}' not found`
});
}
return groups[id];
};

export { getGroupById };

```

Thank you!

Start with docs/rules/exports-last.md and compare its option documentation with docs/rules/newline-after-import.md. Then locate the exports-last rule entry point and its tests, and verify that a configurable count enforces the requested blank lines before the first export without affecting other exports.

Written by the indexing model from the issue text.