refactor: config package

[JeyJeyGao]

type Config struct
    func LoadConfig() (*Config, error)
    func NewConfig() *Config
    func (c *Config) Save() error

type SigningKeys struct
    func LoadSigningKeys() (*SigningKeys, error)
    func NewSigningKeys() *SigningKeys
    func (s *SigningKeys) Save() error
type KeySuite
    func (k KeySuite) Is(name string) bool
type X509KeyPair
type ExternalKey

Please review this PR firstly: #179
Signed-off-by: Junjie Gao junjiegao@microsoft.com

[codecov-commenter]

Codecov Report

Merging #182 (5d8ecf0) into main (75b3248) will increase coverage by 0.45%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##             main     #182      +/-   ##
==========================================
+ Coverage   80.25%   80.71%   +0.45%     
==========================================
  Files          22       22              
  Lines        1722     1711      -11     
==========================================
- Hits         1382     1381       -1     
+ Misses        266      258       -8     
+ Partials       74       72       -2     

Impacted Files	Coverage Δ
config/config.go	44.44% <50.00%> (+12.44%)	⬆️
config/base.go	55.00% <100.00%> (ø)
config/keys.go	36.84% <100.00%> (+2.05%)	⬆️

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[shizhMSFT]

LGTM

[shizhMSFT]

It will be better if we add a package documentation in config.go.

[priteshbandi]

LGTM

[shizhMSFT]

LGTM