connection.ActiveConfig() should use config.Active() instead of reading configuration directly

[timburks]

Fixes #1231

config.Active() supports the --config flag where the previous code for connection.ActiveConfig() does not.

[codecov]

Codecov Report

Merging #1232 (94e5690) into main (f805290) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1232      +/-   ##
==========================================
- Coverage   71.98%   71.91%   -0.07%     
==========================================
  Files         146      146              
  Lines       12241    12250       +9     
==========================================
- Hits         8812     8810       -2     
- Misses       2747     2759      +12     
+ Partials      682      681       -1     

Files	Coverage Δ
pkg/config/config.go	60.49% <100.00%> (+0.74%)	⬆️
pkg/connection/config.go	47.05% <100.00%> (-17.39%)	⬇️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[timburks]

But now this doesn't work:

$ registry --config apiz apply -f .
Usage:
...

Error: open /home/tim/.config/registry/apiz: no such file or directory
Run 'registry --help' for usage.

[timburks]

Now with the latest changes, all of the following work:

# local config file with only a basename
$ registry --config apiz apply -f .
  INFO[0000] Applying apis/petstore    uid=57088557
  INFO[0000] 1 YAML file(s) applied (3 found, 1 with 'apiVersion: apigeeregistry/v1') uid=57088557

# local config file, multisegment path
$ registry --config ./apiz apply -f .
  INFO[0000] Applying apis/petstore    uid=a41eb5db
  INFO[0000] 1 YAML file(s) applied (3 found, 1 with 'apiVersion: apigeeregistry/v1') uid=a41eb5db

# config file in ~/.config/registry
$ mv apiz ~/.config/registry
$ registry --config apiz apply -f .
  INFO[0000] Applying apis/petstore    uid=0a8bbee3
  INFO[0000] 1 YAML file(s) applied (3 found, 1 with 'apiVersion: apigeeregistry/v1') uid=0a8bbee3

[timburks]

Now with tests.