Improve config.Service validation, introduce config.BaseURL

[VojtechVitek]

config.BaseURL

[metadata]
  url = "http://localhost:4242"

package config

import "github.com/0xsequence/go-libs/config"

type MetadataConfig {
    URL config.BaseURL `toml:"url"`
}

// url := config.Metadata.BaseURL.URL()

config.Services

[services.metadata]
    url = "http://localhost:4242"
    jwt_secret = "secret"
    debug_requests = false

[services.indexer]
    url = "https://indexer.sequence.app"
    jwt_secret = "secret"
    access_key = "key"  ## This will error out, as jwt_secret and access_key are mutually exclusive
    debug_requests = true

[services.another]
    disabled = true
    url = ""            ## Empty URL is OK, since the service is disabled
    debug_requests = true

[david-littlefarmer]

LGTM