Allow registry auth config without authority value

[luhring]

Related to anchore/stereoscope#68

Allows Syft to use registry credentials in cases where the user hasn't provided an "authority" config value

[github-actions]

Benchmark Test Results

Benchmark results from the latest changes vs base branch

name                                                   old time/op    new time/op    delta
ImagePackageCatalogers/ruby-gemspec-cataloger-2           979µs ± 3%    1047µs ± 1%  +6.97%  (p=0.008 n=5+5)
ImagePackageCatalogers/python-package-cataloger-2        1.35ms ± 2%    1.45ms ± 3%  +7.74%  (p=0.008 n=5+5)
ImagePackageCatalogers/javascript-package-cataloger-2     521µs ± 1%     542µs ± 3%  +4.16%  (p=0.008 n=5+5)
ImagePackageCatalogers/dpkgdb-cataloger-2                 491µs ± 3%     524µs ± 3%  +6.76%  (p=0.008 n=5+5)
ImagePackageCatalogers/rpmdb-cataloger-2                  517µs ± 4%     546µs ± 2%  +5.57%  (p=0.016 n=5+5)
ImagePackageCatalogers/java-cataloger-2                  6.69ms ± 5%    7.06ms ± 2%  +5.63%  (p=0.032 n=5+5)
ImagePackageCatalogers/apkdb-cataloger-2                  709µs ± 0%     753µs ± 2%  +6.27%  (p=0.016 n=4+5)
ImagePackageCatalogers/go-cataloger-2                     265µs ± 5%     274µs ± 3%    ~     (p=0.095 n=5+5)
ImagePackageCatalogers/rust-cataloger-2                   409µs ± 3%     417µs ± 3%    ~     (p=0.151 n=5+5)

name                                                   old alloc/op   new alloc/op   delta
ImagePackageCatalogers/ruby-gemspec-cataloger-2          97.6kB ± 0%    97.6kB ± 0%    ~     (p=0.222 n=5+5)
ImagePackageCatalogers/python-package-cataloger-2         579kB ± 0%     579kB ± 0%    ~     (p=0.690 n=5+5)
ImagePackageCatalogers/javascript-package-cataloger-2     112kB ± 0%     112kB ± 0%    ~     (p=0.341 n=5+5)
ImagePackageCatalogers/dpkgdb-cataloger-2                 116kB ± 0%     116kB ± 0%    ~     (p=0.421 n=5+5)
ImagePackageCatalogers/rpmdb-cataloger-2                  134kB ± 0%     134kB ± 0%    ~     (p=0.643 n=5+5)
ImagePackageCatalogers/java-cataloger-2                  1.78MB ± 0%    1.78MB ± 0%    ~     (p=0.548 n=5+5)
ImagePackageCatalogers/apkdb-cataloger-2                 1.14MB ± 0%    1.14MB ± 0%    ~     (p=0.389 n=5+5)
ImagePackageCatalogers/go-cataloger-2                    48.4kB ± 0%    48.5kB ± 0%    ~     (p=0.222 n=5+5)
ImagePackageCatalogers/rust-cataloger-2                  89.0kB ± 0%    88.9kB ± 0%  -0.02%  (p=0.008 n=5+5)

name                                                   old allocs/op  new allocs/op  delta
ImagePackageCatalogers/ruby-gemspec-cataloger-2           1.96k ± 0%     1.96k ± 0%    ~     (all equal)
ImagePackageCatalogers/python-package-cataloger-2         5.89k ± 0%     5.89k ± 0%    ~     (all equal)
ImagePackageCatalogers/javascript-package-cataloger-2     1.93k ± 0%     1.93k ± 0%    ~     (all equal)
ImagePackageCatalogers/dpkgdb-cataloger-2                 2.37k ± 0%     2.37k ± 0%    ~     (all equal)
ImagePackageCatalogers/rpmdb-cataloger-2                  3.19k ± 0%     3.19k ± 0%    ~     (all equal)
ImagePackageCatalogers/java-cataloger-2                   22.3k ± 0%     22.3k ± 0%    ~     (all equal)
ImagePackageCatalogers/apkdb-cataloger-2                  1.85k ± 0%     1.85k ± 0%    ~     (all equal)
ImagePackageCatalogers/go-cataloger-2                     1.40k ± 0%     1.40k ± 0%    ~     (all equal)
ImagePackageCatalogers/rust-cataloger-2                   2.75k ± 0%     2.75k ± 0%    ~     (all equal)