atlasaction: move gitlab client to internal package #1338

Job	Run time
migrate-test	13s
golangci-lint	17s
migrate-down	13s
monitoring	40s
schema-apply (lint-review)	8s
schema-plan	10s
schema-plan-approve	0s
schema-apply (on-the-fly, true)	7s
schema-push	9s
schema-apply (remote-repo, atlas://atlas-action/plans/20240910183610, atlas://atlas-action?tag=e2e)	13s
schema-apply (local-plan, file://20240910173744.plan.hcl)	9s
schema-test	10s
schema-apply (multiple-envs, file://20240910173744.plan.hcl)	7s
shim	14s
schema-apply (legacy, v0.27.0, true)	16s
shim-e2e	6s
unit-tests	1m 12s
	4m 24s

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