[Enhancement] - Ability to specify custom buildspec template (or additional parameters in buildspec)

[RamdevWudaliTR]

a use case in an environment where custom libraries are being pulled in from JFrog or even Docker hub, we need to be able to pass in credentials. The typical way of doing this is to specify parameter store keys or Secret store keys that can be used for authenticating. However, it is currently not possible. (unless we modify the code to do something custom. )

Perhaps having additional options to pass in parameter store keys to use for authentication and Also be able to specify a custom buildspec would be great.