[Backport 2024.2] test(customd2): add custom_d2/workload1 test configurations

[mergify]

First configuration is small - 3 DCs, 3 nodes per each.

Second configuration is big - 5DCs, 12 nodes per each.
This big setup never reached the Test start stage
because of the very slow bootstrap process in a multi-dc environment.

Ref: #19131

Testing

• Small (Ok): scylla-staging/valerii/vp-longevity-aws-custom-d2-workload1-multidc#14
• Big (Fail): scylla-staging/valerii/vp-longevity-aws-custom-d2-workload1-multidc-big#5

PR pre-checks (self review)

• I added the relevant backport labels
• I didn't leave commented-out/debugging code

Reminders

• Add New configuration option and document them (in sdcm/sct_config.py)
• Add unit tests to cover my changes (under unit-test/ folder)
• Update the Readme/doc folder relevant to this change (if needed)

(cherry picked from commit 9b9f10e)

Parent PR: #8951