feat: allow empty objects array

[onlined]

Reason for Change:
The YAML for secret provider class can be created by a template engine and all the objects listed there can depend on a template variable to be truthy. In this case, when all of them are falsy, it becomes a special case if empty objects array is not allowed. Example:

objects: |
  array:
{{ if condition1 }}
   - |
     objectName: "Secret1"
     objectType: secret
     objectFormat: pfx
     objectEncoding: base64
{{ end }}
{{ if condition2 }}
   - |
     objectName: "Secret2"
     objectType: secret
     objectFormat: pfx
     objectEncoding: base64
{{ end }}

If condition1 and condition2 are both falsy, the provider returns an error, but simply mounting an empty volume would be more consistent and it doesn't require special handling.

Requirements

• squashed commits
• included documentation
• added unit tests and e2e tests (if applicable).

Issue Fixed:

Does this change contain code from or inspired by another project?

• Yes
• No

Special Notes for Reviewers:

[codecov-commenter]

Codecov Report

Merging #671 (6704e81) into master (b35ae5f) will decrease coverage by 0.65%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #671      +/-   ##
==========================================
- Coverage   62.74%   62.09%   -0.66%     
==========================================
  Files           7        7              
  Lines         765      765              
==========================================
- Hits          480      475       -5     
- Misses        252      257       +5     
  Partials       33       33              

[onlined]

/azp run pr-e2e-azure

[azure-pipelines]

Commenter does not have sufficient privileges for PR 671 in repo Azure/secrets-store-csi-driver-provider-azure

[aramase]

/azp run pr-e2e

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[github-actions]

This PR is stale because it has been open 14 days with no activity. Please comment or this will be closed in 7 days.

[onlined]

@aramase Can you review this? It's OK if we don't merge for some time.

[github-actions]

This PR is stale because it has been open 14 days with no activity. Please comment or this will be closed in 7 days.

[onlined]

@aramase ?

[aramase]

/azp run pr-e2e

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Azure Pipelines successfully started running 1 pipeline(s).

[aramase]

/azp run pr-e2e-azure

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[nilekhc]

lgtm

[aramase]

lgtm

[aramase]

/azp run pr-e2e

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).