Add environment variables for parameters

[zhan9san]

Fix #124

Here is what I tested.

$ cat artifactory-cleanup-1.yaml
# artifactory-cleanup.yaml
artifactory-cleanup:
  server: https://artifactory.example.com/artifactory
  # $VAR is auto populated from environment variables
  user: $ARTIFACTORY_USERNAME
  password: $ARTIFACTORY_PASSWORD

  policies:
    - name: Remove all files from repo-name-here older than 7 days
      rules:
        - rule: Repo
          name: "test-artifacts-local"
        - rule: DeleteOlderThan
          days: 65535

$ env | grep ARTIFACTORY_CLEANUP
ARTIFACTORY_CLEANUP_CONFIG_FILE=artifactory-cleanup-1.yaml
ARTIFACTORY_CLEANUP_DESTROY=True
$ artifactory-cleanup
********************************************************************************
Destroy MODE
Checking 'test-artifacts-local' repository exists.
The test-artifacts-local repository exists.
Add AQL Filter - rule: Repo - Apply the policy to one repository.
Before AQL query: []
After AQL query: [{'repo': {'$eq': 'test-artifacts-local'}}]

Add AQL Filter - rule: DeleteOlderThan - Deletes artifacts older than `` days`` days
Delete artifacts older than 1844-08-08
Before AQL query: [{'repo': {'$eq': 'test-artifacts-local'}}]
After AQL query: [{'repo': {'$eq': 'test-artifacts-local'}}, {'created': {'$lt': '1844-08-08'}}]

Add AQL Text - rule: Repo - Apply the policy to one repository.
Add AQL Text - rule: DeleteOlderThan - Deletes artifacts older than `` days`` days
********************************************************************************
Result AQL Query:
items.find({"$and": [{"repo": {"$eq": "test-artifacts-local"}}, {"created": {"$lt": "1844-08-08"}}]}).include("*", "property", "stat")
********************************************************************************
Found 0 artifacts
Filter artifacts - rule: Repo - Apply the policy to one repository.
Filter artifacts - rule: DeleteOlderThan - Deletes artifacts older than `` days`` days
Found 0 artifacts AFTER filtering
Deleted artifacts count: 0
Summary size: 0

+--------------------------------------------------------+-------------+------+
| Cleanup Policy                                         | Files count | Size |
+--------------------------------------------------------+-------------+------+
| Remove all files from repo-name-here older than 7 days |      0      |  0B  |
|                                                        |             |      |
| Total size: 0B                                         |             |      |
+--------------------------------------------------------+-------------+------+

[allburov]

@zhan9san thank you! 👍