Use UPTEST_CLOUD_CREDENTIALS Github repo secret to enable cross-account resource uptesting

[ulucinar]

Description of your changes

This PR proposes a change that would allow us to utilize a second IAM user for cross-account resource uptesting when the repo is properly configured with a second credentials environment variable.

A second ProviderConfig.aws named peer is provisioned in a different AWS account than the default ProviderConfig's account for cross-account testing.

NOTE: This PR introduces a breaking change in the expected syntax for the Github repo secret UPTEST_CLOUD_CREDENTIALS, and the corresponding env. variable UPTEST_CLOUD_CREDENTIALS when running uptest locally with the associated make targets. It now has the following syntax:

DEFAULT='[default]
aws_access_key_id = REDACTED
aws_secret_access_key = REDACTED'
PEER='[default]
aws_access_key_id = REDACTED
aws_secret_access_key = REDACTED'

So the value of the env. variable is expected to have the DEFAULT key to be used as the default set of credentials, and another optional key named PEER.

I have:

• Run make reviewable test to ensure this PR is ready for review.
• Update the vault key for UPTEST_CLOUD_CREDENTIALS
• Change the syntax of the UPTEST_CLOUD_CREDENTIALS secret Github repo secret and add the second IAM user access credentials with the PEER key.
• Update the vault key for UPTEST_DATASOURCE
• Update the UPTEST_DATASOURCE Github repo secret so that it contains the ID of this second account.

How has this code been tested

A second ProviderConfig.aws named peer is now available in the test runtime:

Please also see: #235

[ulucinar]

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

[turkenh]

Thanks @ulucinar!

[ulucinar]

We sync'ed with @ezgidemirel who is on support rotation today and we decided to update the repo secret UPTEST_CLOUD_CREDENTIALS with the breaking new syntax change tomorrow.