Fix loading session shares that have a plus sign in the sessionId

[cmdcolin]

Fixes #3520

Works

https://share.jbrowse.org/api/v1/load?sessionId=Xc-hrJg1O%2B

Fails

https://share.jbrowse.org/api/v1/load?sessionId=Xc-hrJg1O+

Seems like it should be the same, could fix on the server side perhaps, but this is a client side fix

[cmdcolin]

Loading the example share link from #3520 works on this branch now

[codecov]

Codecov Report

Merging #3524 (13eb956) into main (819526f) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 13eb956 differs from pull request most recent head 11776cd. Consider uploading reports for the commit 11776cd to get more accurate results

@@           Coverage Diff           @@
##             main    #3524   +/-   ##
=======================================
  Coverage   62.57%   62.57%           
=======================================
  Files         862      862           
  Lines       30164    30164           
  Branches     7234     7234           
=======================================
  Hits        18875    18875           
  Misses      11101    11101           
  Partials      188      188           

Impacted Files	Coverage Δ
products/jbrowse-web/src/sessionSharing.ts	23.07% <100.00%> (ø)

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[cmdcolin]

This PR now updates the lambda to replace space char with a plus in the sessionId, to work around the plus sign being interpreted as a space. It also encodesURIComponent too since this is probably proper behavior anyways