Fixathon: Add image alt text

[amansilla]

PR Description

This PR and all included in Core PRs enable Spryker users to set HTML alt text for product images in small and large version.

Steps before you submit a PR

• Please add tests for the code you add if it's possible.
• Please check out our contribution guide: https://docs.spryker.com/docs/dg/dev/code-contribution-guide.html
• Add a contribution-license-agreement.txt file with the following content:
  I hereby agree to Spryker\'s Contribution License Agreement in https://github.com/spryker/product-image/blob/HASH_OF_COMMIT_YOU_ARE_BASING_YOUR_BRANCH_FROM_MASTER_BRANCH/CONTRIBUTING.md.

This is a mandatory step to make sure you are aware of the license agreement and agree to it. HASH_OF_COMMIT_YOU_ARE_BASING_YOUR_BRANCH_FROM_MASTER_BRANCH is a hash of the commit you are basing your branch from the master branch. You can take it from commits list of master branch before you submit a PR.

Checklist

• I agree with the Code Contribution License Agreement in CONTRIBUTING.md

[matweew]

ATM it's major change for the module according to our current rules (each change of DB structure must trigger major release). For minor release, the code should be written in the way the module should work correctly with the old DB structure without new fields.