chore: add root workspace folder to gitignore

[kuhe]

I would like to designate a root /workspace folder as gitignored so I can write scripts inside the folder.

Reason: compatibility with script-runner conventions

SDK developers may find themselves with many scratch files that execute specific SDK behaviors over time when working/triaging issues. For example:

/boto3
  /workspace
    /comparing-perf-v3-v4.py
    /event-listener-check-4566.py
    /s3
      /checksum-testing.py
/other-product-repo
  /workspace
    /dynamodb-test.js
    /s3-test-8723.mjs
/other-product-repo
  /workspace
    /sts-test.php

etc. etc.

These files are not versioned, but can accumulate over time. When working with multiple products and SDKs, the number of workspaces and scratch files multiplies.

The script-runner helper has the following syntax and behavior:

r <fuzzy filename match>

e.g.

r perf 3 4

will match to /workspace/comparing-perf-v3-v4.py and run it with python based on extension matching.

It is programmed to search only the /workspace local folder depending on which repository folder it is being run from. Therefore, I would like to establish /workspace as an ignored folder across SDK products, and distribute the r runner as a developer tool.

The runner script: https://pypi.org/project/workspace-runner/

[kuhe]

PR group:
boto/boto3#4847
aws/aws-sdk-python#95
https://github.com/aws/aws-sdk-php/pull/3352/changes