metadata errors are NOT errors, prettify display

[taylordowns2000]

Closes #812

Notes for the reviewer

@josephjclark , the <Empty /> block doesn't seem to get returned, even when trying to use an adaptor that has no magic.

See my comments below. I was about to put the <Empty /> return after 'no_metadata_result' but realized that this is probably meant to mean something different, so I thought I'd ask.

  if (!metadata) {
    // I never seem to get reached...
    return <Empty adaptor={adaptor} />;
  }
  if (metadata === true) {
    return <div className="block m-2">Loading metadata...</div>;
  }
  if (metadata.error) {
    const { error } = metadata;
    let message = `An error occurred while loading metadata: ${error}`;

    if (error === 'no_credential')
      message =
        "Metadata can only be loaded once you've added a valid credential.";

    if (error === 'no_metadata_result')
      // When I use an adaptor that doesn't have magic, I get this error...
      message = `The ${adaptor} adaptor isn't returning any metadata.`;

    return <div className="block m-2">{message}</div>;
  }

Checklist before requesting a review

• I have performed a self-review of my code
• I have verified that all appropriate authorization policies have been implemented and tested
• If needed, I have updated the changelog
• Taylor has QA'd this feature

[codecov]

Codecov Report

Patch coverage: 66.66% and project coverage change: -0.05 ⚠️

Comparison is base (79492a1) 92.68% compared to head (92a1085) 92.64%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #811      +/-   ##
==========================================
- Coverage   92.68%   92.64%   -0.05%     
==========================================
  Files         163      163              
  Lines        3911     3916       +5     
==========================================
+ Hits         3625     3628       +3     
- Misses        286      288       +2     

Impacted Files	Coverage Δ
lib/lightning/cli.ex	100.00% <ø> (ø)
lib/lightning/metadata_service.ex	62.50% <66.66%> (-0.47%)	⬇️

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