add opentelemetry output

[evanzhang87]

use add_fields to build formatted fields, then send to OLPT server, just support log now

const (
	resourcePrefix       = "oltp_resource_"
	scopePrefix          = "oltp_scope_"
	scopeName            = "oltp_scope_name"
	scopeVersion         = "oltp_scope_version"
	scopeSchemaUrl       = "oltp_scope_schemaurl"
	recordPrefix         = "oltp_logrecords_"
	recordTime           = "oltp_logrecords_time"
	recordSeverity       = "oltp_logrecords_severity"
	recordSeverityNumber = "oltp_logrecords_severitynumber"
	recordFlags          = "oltp_logrecords_flags"
	recordTraceId        = "oltp_logrecords_traceid"
	recordSpanId         = "oltp_logrecords_spanid"
	recordBody           = "oltp_logrecords_body"
)

type OLTPOutputConfig struct {
	ServiceAddress string `json:"service_address"` // default localhost:4317
	ClientAuthConfig
	Timeout     int               `json:"timeout"` // default 5s
	Compression string            `json:"compression"` // default none
	Headers     map[string]string `json:"headers"` // grpc headers
}

type ClientAuthConfig struct {
	TLSCA               string `json:"tls_ca"`
	TLSCert             string `json:"tls_cert"`
	TLSKey              string `json:"tls_key"`
	TLSKeyPwd           string `json:"tls_key_pwd"`
	TLSMinVersion       string `json:"tls_min_version"`
	InsecureSkipVerify  bool   `json:"insecure_skip_verify"`
	ServerName          string `json:"tls_server_name"`
	RenegotiationMethod string `json:"tls_renegotiation_method"`
	Enable              *bool  `json:"tls_enable"`
}

update GoVersion to 1.19, it's needed by opentelemetry, and 1.13 was too old, it's time to try new GO!

[childe]

Thanks very much for your PR, but according to my current plan, I'm not intending to add any more OUTPUTs. If you could provide a plugin-style codec & output, I'm pleased to add its link to Readme.

PS: refer to https://go.dev/ref/mod#go-mod-file-go:

The go directive sets the minimum version of Go required to use this module.

[codecov-commenter]

Codecov Report

Attention: 188 lines in your changes are missing coverage. Please review.

Comparison is base (5c04854) 32.62% compared to head (566c3ba) 31.96%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #234      +/-   ##
==========================================
- Coverage   32.62%   31.96%   -0.66%     
==========================================
  Files          53       55       +2     
  Lines        4377     4611     +234     
==========================================
+ Hits         1428     1474      +46     
- Misses       2794     2973     +179     
- Partials      155      164       +9     

Flag	Coverage Δ
unittests	31.96% <19.65%> (-0.66%)	⬇️

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Files	Coverage Δ
codec/oltp_encoder.go	0.00% <0.00%> (ø)
output/oltp_output.go	29.11% <29.11%> (ø)

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[evanzhang87]

That's ok, learn from you!