feat(did-resolver): simplify DIDResolverPlugin constructor

[mirceanis]

What issue is this PR fixing

fixes #976

What is being changed

The DIDResolverPlugin now accepts a map of DIDResolver implementations as well, to simplify user required dependencies, config, and constructor.

If a resolver argument is provided, it will get used instead of the mapping to ensure backward compatibility and allow users to make extra configuration.

old version:

import { Resolver } from 'did-resolver'

new DIDResolverPlugin({
  resolver: new Resolver({
    ...ethrResolver(),
    ...keyResolver(),
    ...ionResolver()
  })
})

new version:

new DIDResolverPlugin({
  ...ethrResolver(),
  ...keyResolver(),
  ...ionResolver()
})

Quality

Check all that apply:

• I want these changes to be integrated
• I successfully ran yarn, yarn build, yarn test, yarn test:browser locally.
• I allow my PR to be updated by the reviewers (to speed up the review process).
• I added unit tests.
• I added integration tests. (updated localAgent.test.ts to use the new config)
• I did not add automated tests because _________, and I am aware that a PR without tests will likely get rejected.

[codecov]

Codecov Report

Merging #986 (f1033a8) into next (a110e96) will increase coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head f1033a8 differs from pull request most recent head 9f15d81. Consider uploading reports for the commit 9f15d81 to get more accurate results

@@            Coverage Diff             @@
##             next     #986      +/-   ##
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+ Coverage   80.25%   80.28%   +0.02%     
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  Files         118      118              
  Lines        4056     4062       +6     
  Branches      875      877       +2     
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+ Hits         3255     3261       +6     
  Misses        798      798              
  Partials        3        3