[Go] Update go-echo-server generator to respect the --git-host argument

[osechet]

Hi!
As discussed in #15636, this PR changes the template files of go-echo-server in order to respect the --git-host argument. The changes have been tested by running the ./bin/generate-samples.sh ./bin/configs/go-echo-server-petstore-new.yaml and by hand using the generated openapi-generator-cli.jar.

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[wing328]

LGTM. thanks for the PR.