making compress_file_gzip_base64 to be deterministic

[itai1357]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Description

getting compressed-result, where the compression is deterministic (adding mtime=0 makes it by adding to the result some fixed timestamp. when omitting it (or setting None), the result are affected by the current timestamp

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] I have added tests that prove my feature, policy, or fix is effective and works
• [x] New and existing tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules