feat: Add AtCoder integration

[cohu-dev]

Please remember the Contributing Guidelines :heart:

:star2: What does this PR do?

Adds the timer to AtCoder, in the header in only contest page. Please review code 🙏

AtCoder is competitive programming sites.

I tested on both Chrome and Firefox and worked correctly.

Screenshots below are taken in https://atcoder.jp/contests/abc261.

Contest top page

Input only contest title.

Contest problem page

Input problem title and contest title.

:bug: Recommendations for testing

All changes should be tested across Chrome and Firefox.

:memo: Links to relevant issues or information