Jsonlines append mode
**Description**: Adding support to append mode for `to_json` when 'orient' is `records` and 'lines' is `True`

**Motivation**: [jsonlines](http://jsonlines.org/) is a format that is gaining some space (e.g. [Cloud Storage](https://cloud.google.com/bigquery/docs/loading-data-cloud-storage-json)). In pandas It's achieved using `to_json` with `orient='records'` and `lines=True`. But `to_json` doesn't have the option to use `mode='a'` to append to a file, this PR aims to provide a simple append mode for jsonlines using pandas.

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- [X] closes #35849
- [X] tests added / passed
- [X] passes `black pandas`
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. > This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this.

I'm moving to another country and It's been hard to find time to work on the proposed changes but please don't close this PR, I'll update as soon as I find time to work on It again. > > This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this.
> 
> I'm moving to another country and It's been hard to find time to work on the proposed changes but please don't close this PR, I'll update as soon as I find time to work on It again.

No problem! We'll keep this open @arw2019 is there a reference on proper way of adding tests on pandas? > @arw2019 is there a reference on proper way of adding tests on pandas?

Not really. Take a look at similar tests in the `pandas/tests/io/json` for a general idea of the format. Typically the pattern we use is:
- construct result
- construct expected result
- assert the two are equal

 If you push an attempt we'll give you detailed pointers This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. Sorry, I'm not having time to work on this and probably will not be able to do for a while. I'll close the PR to give the chance of other people to work on this. Anyone feel free to fork my repo and continue