Add new script to start optimiser for developers

[thejus03]

Context

• Fixes #4247

Implementation

• Added a new global variable called OPTIMISER_API_URL
• Depending on the script that is run it assigns either http://localhost:8020/optimise or api/optimiser/optimise
• Added a new script called yarn start:local for running the localhost api endpoint on the website
• Updated the yarn start script to include the real endpoint for production
• Updated the optimiser README to reflect the above changes

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[codecov[bot]]

Codecov Report

:x: Patch coverage is 0% with 1 line in your changes missing coverage. Please review. :white_check_mark: Project coverage is 55.14%. Comparing base (988c6fd) to head (426b592). :warning: Report is 152 commits behind head on master.

Files with missing lines	Patch %	Lines
website/src/apis/optimiser.ts	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4263      +/-   ##
==========================================
+ Coverage   54.52%   55.14%   +0.62%     
==========================================
  Files         274      297      +23     
  Lines        6076     6729     +653     
  Branches     1455     1619     +164     
==========================================
+ Hits         3313     3711     +398     
- Misses       2763     3018     +255     

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