- `aws-sdk-go` has [a vuln](https://osv.dev/vulnerability/GO-2022-0646) in the v1 EncryptionClient
  - it's fixed in the v2 client
  - we don't use this functionality, but still get reported this vuln
    - instead add an ignore for the vuln, figured I might as well make the upgrade to v2
- confirmed that `go.mod` has latest versions (e.g. `config` [released v1.19.0](https://github.com/aws/aws-sdk-go-v2/releases/tag/release-2023-10-16) this week)

- follow the [migration instructions](https://aws.github.io/aws-sdk-go-v2/docs/migrating/)
  - migrate all `session` usage to `config.LoadDefaultConfig` per [instructions](https://aws.github.io/aws-sdk-go-v2/docs/migrating/#configuration-loading)
    - this includes shared config handling, so I believe `session.SharedConfigEnable` is no longer necessary per [instructions](https://aws.github.io/aws-sdk-go-v2/docs/migrating/#migrating-from-newsessionwithoptions)
      - the docs on ["Speciyfing Credentials"](https://aws.github.io/aws-sdk-go-v2/docs/configuring-sdk/#specifying-credentials) seem to state this as well, if I'm understanding correctly
    - see also `config.WithRegion` mention in the [instructions](https://aws.github.io/aws-sdk-go-v2/docs/migrating/#migrating-from-newsession-with-awsconfig-options)
  - migrate credential usage
    - [`Config.Credentials`](https://pkg.go.dev/github.com/aws/aws-sdk-go-v2/aws#Config) still exists, but the function is now [`Retrieve(context)`](https://pkg.go.dev/github.com/aws/aws-sdk-go-v2/aws#CredentialsProvider) instead of `Get`
      - the [`Credentials` struct](https://pkg.go.dev/github.com/aws/aws-sdk-go-v2/aws#Credentials) otherwise looks the same, has the `AccessKeyId`, `SecretAccessKey`, and `SessionToken` that were used in v1
    - STS credentials are retrieved a bit differently now [per instructions](https://aws.github.io/aws-sdk-go-v2/docs/migrating/#aws-security-token-service-credentials)
      - use a `config` instead of a `session` to create a client, then use `NewAssumeRoleProvider` instead of `NewCredentials

- NOTE: I used `context.Background()` for all of the contexts that are now required
  - it may make more sense for context to be passed into these functions, but that would be a breaking change and require downstream changes in Argo projects, so I left that out for now and just went with `Background` as a default

Signed-off-by: Anton Gilgur <[email protected]>

- this was just straight up missing from the migration guide's imports
  - found it myself: https://pkg.go.dev/github.com/aws/aws-sdk-go-v2/service/sts

Signed-off-by: Anton Gilgur <[email protected]>

- more idiomatic Go, less memory use, and makes it easier to replace with an argument later

Signed-off-by: Anton Gilgur <[email protected]>