Fix the fullname of sidekiq to use the "fullname" template helper function

What does this MR do?

It makes sidekiq use the name as defined by the "fullname" helper function. When overriding the "fullname" in a higher chart, sidekiq breaks as it uses "fullname" for configmaps but does not use "fullname" when referencing it. In addition it's impossible to change the sidekiq deployment name.

Related issues

Closes: #3226 (closed)

Checklist

See Definition of done.

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Required

• Merge Request Title and Description are up to date, accurate, and descriptive
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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.