Update identity documentation

[nambrot]

Description

This PR updates the documentation related to identity, specifically

• The changes for the off-chain reveal as well as the wait for selectIssuers
• Metadata and how to use it.

This PR did not update the graphic on the page, nor does it include instructions on how to deploy and run the attestation service which is left for @aaitor in #1077

Related issues

• Fixes Users should be able to reference updated documentation on identity #1784

[codecov]

Codecov Report

Merging #1790 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master    #1790    +/-   ##
========================================
  Coverage   74.45%   74.45%            
========================================
  Files         281      281            
  Lines        7817     7817            
  Branches      973      685   -288     
========================================
  Hits         5820     5820            
  Misses       1880     1880            
  Partials      117      117

Flag	Coverage Δ
#mobile	74.45% <ø> (ø)	⬆️

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