Add append and replace load strategies with example DAG for Table

[sunank200]

Description

What is the current behavior?

Although the logic for the replace and append is implemented this is not working because if_exists is not propagated from TransferParams here: https://github.com/astronomer/apache-airflow-provider-transfers/blob/main/src/universal_transfer_operator/data_providers/database/base.py#L202

closes: #47

What is the new behavior?

• Add append and replace load strategies with example DAG for Table
• Add example DAGs
• Add docs
• Test is already there to test the behaviour

Does this introduce a breaking change?

No

Checklist

• [x] Created tests which fail without the change (if possible)
• [x] Extended the README / documentation, if necessary

[sunank200]

[utkarsharma2]

Can we add test cases to validate the behavior?

1. Append to table
2. Replace to table

[sunank200]

Add tests

Added the tests: https://github.com/astronomer/apache-airflow-provider-transfers/pull/45/commits/9d9f5e8427ec66092341e4fb60f4205fb55ecebb