Set gitaly to use ssd storage class for new deployment

What does this MR do?

Check if there is an existing review app deployment.

1. If there is, do not set a ssd gitaly storage class
2. If there is not, we can set a ssd gitaly storage class

For existing deployments that have not had an upgrade attempt to use ssd, this will allow them to be deployed. There would not be change to the existing stateful set.

For existing deployments that already have a failed upgrade attempt to use ssd, this may work, if helm sees that there is no difference in the stateful set. Otherwise, we'd still need to manually rollback helm to the state before it has ssd, or remove the deployment altogether.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
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• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
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• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team