feat(vpc-rtb-r): added examples for routetable and route + selector/ref

[haarchri]

Signed-off-by: haarchri chhaar30@googlemail.com

Description of your changes

• added example for routetable without inline route
• added example for route
• added ref/selector for gateway_id in route for internetgateway
• adopted example for internetgateway to fits vpc & providerConfig

Fixes #184

I have:

• [x] Read and followed Crossplane's contribution process.
• [x] Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

NAME                                                READY   SYNCED   EXTERNAL-NAME           AGE
internetgateway.ec2.aws.jet.crossplane.io/example   True    True     igw-04366bf2a1d995e23   12m

NAME                                              READY   SYNCED   EXTERNAL-NAME           AGE
routetable.ec2.aws.jet.crossplane.io/sample-rtb   True    True     rtb-05f0d401bdd1da796   23m

NAME                                       READY   SYNCED   EXTERNAL-NAME           AGE
vpc.ec2.aws.jet.crossplane.io/sample-vpc   True    True     vpc-09dd37af4a9019ef2   44m

NAME                                           READY   SYNCED   EXTERNAL-NAME                       AGE
route.ec2.aws.jet.crossplane.io/sample-route   True    True     r-rtb-05f0d401bdd1da7961080289494   11m