:hammer: Remove Kustomize

[diegoluisi]

Thank you for making devxp-tech/backstage better

What kind of change does this PR introduce?

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update (formatting)
• [ ] Refactoring (no functional changes)
• [ ] CI related changes
• [ ] Other... Please describe:

What is the current behavior?

What is the new behavior?

Does this PR introduce a new API versioning or breaking change?

• [ ] Yes
• [ ] No

Other information

Also verify you have:

• [ ] Read the contributions page.
• [ ] Read the DCO, if you are a first time contributor.
• [ ] Read the [code of conduct](Code of Conduct).