✨[RUM-2158] Allow more flexible proxy URL

[bcaudan]

Motivation

As discussed in #2429 and #2471, the current proxy strategy with the ddforward parameter, storing the target path and parameters, can be challenging to implement.

A solution allowing to have the path and parameters appended to the provided proxy URL was initially discarded since one of our URL pattern was already blocked, cf easylist.
However, some customers may want to use a proxy regardless of the privacy blocking or could want to tweak themselves the final proxy url to prevent the blocking.

Changes

Allow to pass a function to the proxy init parameter:

init({
  ...
  proxy: (options: {path: string, parameters: string}) => 
    `https://proxy.io/prefix${options.path}/suffix?${options.parameters}`
})

With:

• path: /api/vX/product
• parameters: xxx=yyy&zzz=aaa

Testing

• Local
• Staging
• Unit
• End to end

---

I have gone over the contributing documentation.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b68f949) 93.24% compared to head (a2bce47) 93.24%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2502   +/-   ##
=======================================
  Coverage   93.24%   93.24%           
=======================================
  Files         222      222           
  Lines        6660     6662    +2     
  Branches     1466     1467    +1     
=======================================
+ Hits         6210     6212    +2     
  Misses        450      450           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[hermanbanken]

Thanks @bcaudan!