Rename VUE_APP_TRANSPORT and support VUE_APP_MATRIX_LIST_URL envvar

[andrevmatos]

Fixes #2002

Short description

• Rename VUE_APP_TRANSPORT to VUE_APP_MATRIX_SERVER to avoid conflict with previous var
• Add VUE_APP_MATRIX_LIST_URL:
  • passed to SDK's matrixServerLookup config
  • Has less priority than VUE_APP_MATRIX_SERVER, so make sure that's unset if one wants to iterate over the list in case of the first server isn't responding properly
  • Should be set to a URL ofa file containing a yaml-like list of servers, e.g.: https://raw.githubusercontent.com/raiden-network/raiden-service-bundle/master/known_servers.main.yaml

Definition of Done

• Steps to manually test the change have been documented
• Acceptance criteria are met
• Change has been manually tested by the reviewer (dApp)

Steps to manually test the change (dApp)

[andrevmatos]

@agatsoh this should allow you to set the mainnet's known_server's list URL, and the client will sort them by response times for you, and also try next if one server is failing or not CORS-enabled.
Make sure to unset the previous transport var (not only set it to empty)

[taleldayekh]

Go for it!

[codecov]

Codecov Report

Merging #2009 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2009   +/-   ##
=======================================
  Coverage   95.78%   95.78%           
=======================================
  Files         154      154           
  Lines        5831     5831           
  Branches     1105     1105           
=======================================
  Hits         5585     5585           
  Misses        186      186           
  Partials       60       60           

Flag	Coverage Δ
#dapp	92.55% <ø> (ø)
#sdk	97.08% <ø> (ø)
#sdk_e2e	65.89% <ø> (-0.13%)	⬇️
#sdk_unit	85.93% <ø> (ø)

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Impacted Files	Coverage Δ
raiden-dapp/src/services/raiden-service.ts	88.88% <ø> (ø)

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