[enhancement] Adding new feature for supporting self-signed certificate

Summary

This feature provides a supporting self-signed certificate and Mutual TLS (Related to #568, #900). These changes contain adding volume, volumeMount, and options section in the API resource. Also, you can mount volume and use environment variables to fill the required certificate.
Adding option in operator and restic for using a dir for store temporary files (like generate client pem from client.key and client.crt according to --tls-client-cert option)
Adding more e2e tests to make sure all things are okay (for adding self-signed feature)
Fixing bug about checking errors in the s3 channel when an error is emitted in the channel (File: restic/cli/restore.go). In this scenario after the error happens in s3 connection, the restore pod is frozen because the go routing never realize about this error
Complete document about how to use self-signed issue
Adding variable GO_EXEC in Makefile to choose different versions of Golang (If the user installs multiply versions of Golang)

[x] Categorize the PR by setting a good title and adding one of the labels: bug, enhancement, documentation, change, breaking, dependency as they show up in the changelog
[x] PR contains the label area:operator
[x] Link this PR to related issues
[x] I have not made any changes in the charts/ directory.

[ ] Categorize the PR by setting a good title and adding one of the labels: bug, enhancement, documentation, change, breaking, dependency as they show up in the changelog
[ ] PR contains the label area:chart
[ ] PR contains the chart label, e.g. chart:k8up
[ ] Variables are documented in the values.yaml using the format required by Helm-Docs.
[ ] Chart Version bumped if immediate release after merging is planned
[ ] I have run make chart-docs
[ ] Link this PR to related code release or other issues.