Update lb_loadbalancer_v3.md

[dombisza]

Summary of the Pull Request

hello there,

I have added a hint about l4_flavor and l7_flavor, because the behaviour was really confusing at first.
How it is actually working is:

l4_flavor and l7_flavor empty

• both will be attached with the default flavor (doubles your ELB cost)

l4_flavor or l7_flavor is specified

• only the one you specify gets attached to the ELB

PR Checklist

• Refers to: #xxx
• Tests added/passed.
• Documentation updated.
• Schema updated.
• Release notes added.

Acceptance Steps Performed

=== RUN   TestAccSomethingV0_basic
--- PASS: TestAccSomethingV0_basic (101.71s)
=== RUN   TestAccSomethingV0_timeout
--- PASS: TestAccSomethingV0_timeout (128.67s)
PASS

Process finished with exit code 0

[otc-zuul]

Build succeeded.
https://zuul.otc-service.com/t/eco/buildset/70ca7b9000f3403c9ce711afd9a6cda7

✔️ build-otc-releasenotes SUCCESS in 6m 33s
✔️ noop SUCCESS in 0s
✔️ otc-golangci-lint SUCCESS in 3m 06s
✔️ golang-make-test SUCCESS in 5m 01s
✔️ golang-make-vet SUCCESS in 3m 52s
✔️ tflint SUCCESS in 3m 10s
✔️ goreleaser-build SUCCESS in 7m 15s
✔️ otc-terraform-visualize-main SUCCESS in 6m 23s