feat(cli): show repo and current tag name in "cog log"

[renaultfernandes]

I've made changes to cog log so that it uses "repo_name:latest_tag" instead of the string "cog log" as the file name to pager.

Open Questions:

1. Should we include the current branch name as well. If yes, how should the text be formatted?
2. If there is no tag in the repo, then we only display the repo name. This behavior should be alright, right?
3. I've added code to use the string "cog log" just in case something goes wrong. Should I get rid of it or could you please suggest a better approach to handle this.

Closes #47

[oknozor]

Hello @renaultfernandes thank you for taking this one !
You could add your git signature/github username to cog.toml (in this PR).

1. Should we include the current branch name as well. If yes, how should the text be formatted?

That would be great ! Something like {repo_name} on {branch} {tag} would do I guess.

2. If there is no tag in the repo, then we only display the repo name. This behavior should be alright, right?

Yep.

3. I've added code to use the string "cog log" just in case something goes wrong. Should I get rid of it or could you please suggest a better approach to handle this.

Seems good to me.

I will merge when you complete those little changes.

[renaultfernandes]

Thanks for reviewing my PR. I've made the suggested changes.
Cheers !!!

[oknozor]

Congrats @renaultfernandes, nice one !