datacube: allow passing in URL template

[akphi]

• [x] datacube: allow passing in URL template to make integration with VSCode extension more seamless
• [x] repl: allow passing in initialization message to make integration with VSCode extension more seamless

[github-actions[bot]]

Test Results

  1 022 files  +  1 022    1 022 suites  +1 022   1h 23m 9s :stopwatch: + 1h 23m 9s 12 131 tests +12 131  12 041 :heavy_check_mark: +12 041  90 :zzz: +90  0 :x: ±0  17 560 runs  +17 560  17 470 :heavy_check_mark: +17 470  90 :zzz: +90  0 :x: ±0 

Results for commit 6bbef3f1. ± Comparison against base commit b0dd5fb3.