add env variable for frontend url to remove hardcoded references to i…

[YashK2005]

Main Things

1. Added a FRONTEND_URL env variable to remove hardcoded references to localhost:3000 in our backend.

2. In the welcome page, there was a "You can learn more about the program here" button that before didn't take us anywhere. Now it will take us to either 'https://www.bloodcancers.ca/first-connection-peer-support-program' or 'https://www.cancersdusang.ca/programme-de-soutien-par-les-pairs-premier-contact' depending on the user's language.

3. Added a ENV env variable that should be set to either development or production. Updated seeder so that when ENV=production, it won't seed our mock users and ranking preferences.

4. Updated list of allowed admins to include 5 ppl from LLSC (Megan, Caroline, 3 others)

Please update your env files to have the new FRONTEND_URL and ENV environment variables.

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• My PR name is descriptive and in imperative tense
• My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• I have run the appropriate linter(s)
• I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR