fix(nx-plugin): update rxjs dependency

[goetzrobin]

the analogjs repo has an rxjs version of 7.8.0, we should install the same version when initializing a new nx analog workspace.

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/analogjs/analog/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

Which package are you modifying?

• vite-plugin-angular
• vite-plugin-nitro
• vitest-angular
• astro-angular
• create-analog
• router
• platform
• content
• nx-plugin
• trpc

What is the current behavior?

outdated rxjs version is installed

Closes #

What is the new behavior?

same rxjs version as in main repo is installed

Does this PR introduce a breaking change?

• Yes
• No

Other information

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