Add v1 provider aliases for legacy providers

[dominikschubert]

Since we currently have been advertising the newer provider implementations as v2, users might try to "revert" to the legacy provider by setting the PROVIDER_OVERRIDE_<svc> variable to v1. Unfortunately this will currently fail since they need to remove the variable completely.

This PR now introduces v1 aliases for the legacy (currently still default) providers with a v2 provider, i.e. lambda, s3 and stepfunctions

cc @bentsku @dfangl

[coveralls]

Coverage: 85.094% (-0.01%) from 85.109% when pulling ff0594a on add-v1-provider-aliases into 3cb5069 on master.

[github-actions]

LocalStack integration with Pro

       2 files   -     1         2 suites   - 1   1h 43m 7s ⏱️ +47s
1 798 tests ±    0  1 413 ✔️  -     3  385 💤 +    3  0 ❌ ±0 
2 153 runs   - 371  1 588 ✔️  - 202  565 💤  - 169  0 ❌ ±0 

Results for commit ff0594a. ± Comparison against base commit 3cb5069.

[thrau]

great idea! we'll probably see this pattern a few more times moving forward, so maybe makes sense to introduce this as first class citizen into the provider plugins.