load extensions during compile time using go build tags

[charithabandi]

With the changes in the PR, the action extensions can be loaded and baked into kwild during compile time.
We still support remote extensions, that users can create and deploy using docker.
Support for users to create extensions locally and register them to the extension registry.

Included maths extensions with build tag "ext_test", it's similar to the existing remote math extension. Updated the test scripts to create instances and execute methods on both local "maths" and remote "math" extensions.

[brennanjl]

A few pieces of feedback:

• Some things, particularly regarding remote extensions, should be in internal, and not extensions/action. If the client doesn't need it, then it should go in internal.

• I can see that a lot of code was ported over / used from the https://github.com/kwilteam/kwil-extensions repo. I think this is fine, but we should either:

a. have an extensions/action/utils repo, where this is contained, or
b. include it all in one file.

The expectation right now is that a user would register by importing a file and registering it here. Having many files that implement the functionality that they need to navigate around is weird.

• The math extension example should be given a build tag. We don't want a random math extension included in all of our builds.

[jchappelow]

Sorry, this is an incomplete and speculative review. I will return to it asap.