update Go module to contain /v2

[erhancagirici]

Description of your changes

This PR allows importing the provider as a go module when requiring with v2.x.x semantic version tags.
This was only possible with workaround using go mod -replace and pseudo-versions.

require (
     github.com/upbound/provider-aws/v2 v2.x.y
     ...
)

or

go get github.com/upbound/provider-aws/v2@v2.x.y

• Update Go module path declaration in go.mod to contain /v2
• Update import paths in .go files with new module path reference
• Update PROJECT_REPO to contain /v2 in Makefile, because it also sets the module path prefixes in make targets, used for package discovery for unit tests etc.

Fixes #1865

I have:

• Read and followed Crossplane's contribution process.
• Run make generate and committed the results (ideally in a separate commit).
• Not made any manual changes to generated files, and verified this with make check-diff.

How has this code been tested

CI and Uptest
Uptest-examples/ec2/cluster/v1beta1/vpc.yaml
Uptest-examples/s3/cluster/v1beta2/bucket.yaml
Uptest-examples/ec2/namespaced/v1beta1/vpc.yaml

[erhancagirici]

/test-examples="examples/ec2/cluster/v1beta1/vpc.yaml"

[erhancagirici]

/test-examples="examples/s3/cluster/v1beta2/bucket.yaml"

[erhancagirici]

/test-examples="examples/ec2/namespaced/v1beta1/vpc.yaml"

[sergenyalcin]

Thanks @erhancagirici LGTM!

[erhancagirici]

/test-examples="examples/ec2/cluster/v1beta1/vpc.yaml"

[erhancagirici]

/test-examples="examples/s3/cluster/v1beta2/bucket.yaml"

[erhancagirici]

Note: The local-deploy job is failing due to no space left on device error. It is passing locally, and all the uptest runs also passed (those cover the local-deploy test), along with other CI jobs.