Load empty db with AF 1.10.14 schema instead of running an init job (GoogleCloudPlatform#6527)

Definition of sql_dump_of_empty_airflow_1_10_14_database_for_postgres_13 is
automatically generated sql dump of empty database with AF 1.10.14 schema
compatible with Postgres 13. This is incorporated into the source code as the
whole thing is distributed as a single file.

This change actually simplifies the whole process as it significantly decreases
number of API calls. We're just creating the database and we're letting
Postgres read the sql dump instead of running a new job in GKE and then
removing some rows table by table. As a result we expect the script to be even
more robust.

[CL](cl/388109569) - RC w/ internal passing test will be put in the internal python sample owners chat

## Description

Fixes #<ISSUE-NUMBER>

Note: It's a good idea to open an issue first for discussion.

## Checklist
- [X] I have followed [Sample Guidelines from AUTHORING_GUIDE.MD](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md)
- [ ] README is updated to include [all relevant information](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#readme-file)
- [ ] **Tests** pass:   `nox -s py-3.6` (see [Test Environment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#test-environment-setup))
- [ ] **Lint** pass:   `nox -s lint` (see [Test Environment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#test-environment-setup))
- [ ] These samples need a new **API enabled** in testing projects to pass (let us know which ones)
- [ ] These samples need a new/updated **env vars** in testing projects set to pass (let us know which ones)
- [X] Please **merge** this PR for me once it is approved.
- [ ] This sample adds a new sample directory, and I updated the [CODEOWNERS file](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/.github/CODEOWNERS) with the codeowners for this sample

Author: jacek-izykowski