add handling for postgresql-missing-dictionaries in entrypoint

[itihas]

This PR adds handling for postgresql_missing_dicotinaries. This option changes zulip.conf and needs to be set for initialization to succeed.

Fixes: #371

Tooling tips: https://zulip.readthedocs.io/en/latest/tutorials/screenshot-and-gif-software.html
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How did you test this PR?

Built an image with the new option, set it, and spun up a zulip. It successfully initializes against an external postgresql instance that doesn't have tsearch-extras.

Self-review checklist

• Self-reviewed the changes for clarity and maintainability
  (variable names, code reuse, readability, etc.).

Communicate decisions, questions, and potential concerns.

• Explains differences from previous plans (e.g., issue description).
• Highlights technical choices and bugs encountered.
• Calls out remaining decisions and concerns.
• Automated tests verify logic where appropriate.

Individual commits are ready for review (see commit discipline).

• Each commit is a coherent idea.
• Commit message(s) explain reasoning and motivation for changes.

Completed manual review and testing of the following:

• Visual appearance of the changes.
• Responsiveness and internationalization.
• Strings and tooltips.
• End-to-end functionality of buttons, interactions and flows.
• Corner cases, error conditions, and easily imagined bugs.