Investigate and generate the test certs dynamically instead of storing them in the repository

[prkalle]

Bug description
The certs used for testing may cause security vulnerability alerts though they are only used for testing. To avoid these alerts, we should investigate and implement the changes to generate the test certs (for both cosign keys and also localhost CA cert) locally and use them for testing

One possible solution would be :
While user chooses to start the local test central repository

• Generate the the local test central repository endpoint CA cert could be generate dynamically with make target
• Generate the co-sign key pair dynamically and just sign the only the repository that is being used instead of signing them before hand and storing in the registry content

Expected behavior
Certs used for testing should be generated locally instead of storing them in github.

Steps to reproduce the bug / Relevant debug output

Output of tanzu version

Environment where the bug was observed (cloud, OS, etc)