feat: Add srcset support (#30)

## Description
<!-- Include a summary of the change made and also list the dependencies
that are required if any -->
This PR includes a support for `srcset` urls to be transformed to
cloudinary urls
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## Issue Ticket Number
Fixes [#8]

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## Type of change
<!-- Please select all options that are applicable. -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [x] This change requires a documentation update

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# Checklist:
- [x] I have followed the contributing guidelines of this project as
mentioned in [CONTRIBUTING.md](/CONTRIBUTING.md)
- [ ] I have created an
[issue](https://github.com/colbyfayock/netlify-plugin-cloudinary/issues)
ticket for this PR
- [x] I have checked to ensure there aren't other open [Pull
Requests](https://github.com/colbyfayock/netlify-plugin-cloudinary/pulls)
for the same update/change?
- [x] I have performed a self-review of my own code
- [ ] I have run tests locally to ensure they all pass
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes needed to the documentation

Co-authored-by: colbyfayock <[email protected]>

Author: shikhar13012001