feat: improve error logs when running sync/diff/validate

[GGabriele]

Currently decK doesn't return very useful and descriptive
errors when configuration files are validated. This is
particularly painful when the configuration is distributed
in several files and the error doesn't specificy which
file contains the error.

Let's take for example the following files:

$ cat services.yaml
services:
- name: svc1
  host: mockbin.org
  foo: bar

consumers:
- username: good
- name: bad

If we run decK, it will return some obscure and incomplete errors:

$ deck sync -s services.yaml -s consumers.yaml
Error: reading file: validating file content: 1 errors occurred:
        services.0: Additional property foo is not allowed

This commit is going to improve the way decK handles
configuration validation error logging in order to provide
a more useful description of the problems.
When running decK with the new functionality, the following will
be returned:

$ ./deck sync -s services.yaml -s consumers.yaml
Error: 2 errors occurred:
	reading file services.yaml: validating file content: 1 errors occurred:
	validation error: object="bar", err=services.0: Additional property foo is not allowed

	reading file consumers.yaml: validating file content: 3 errors occurred:
	validation error: object={"name":"bad"}, err=consumers.1: Must validate at least one schema (anyOf)
	validation error: object={"name":"bad"}, err=consumers.1: username is required
	validation error: object="bad", err=consumers.1: Additional property name is not allowed

[codecov-commenter]

Codecov Report

Patch coverage: 78.57% and project coverage change: +0.02 🎉

Comparison is base (d19b622) 33.97% compared to head (a07c5d8) 33.99%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #976      +/-   ##
==========================================
+ Coverage   33.97%   33.99%   +0.02%     
==========================================
  Files         100      100              
  Lines       11906    11906              
==========================================
+ Hits         4045     4048       +3     
+ Misses       7468     7464       -4     
- Partials      393      394       +1     

Impacted Files	Coverage Δ
file/validate.go	82.35% <57.14%> (-7.65%)	⬇️
file/readfile.go	85.36% <85.71%> (+0.24%)	⬆️

... and 2 files with indirect coverage changes

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