Add Octal to Decimal Conversion

[cyrixninja]

Description

Added Octal to Decimal Conversion

References -
https://the-algorithms.com/algorithm/octal-to-decimal
https://www.rapidtables.com/convert/number/octal-to-decimal.html

Wikipedia -

1. https://en.wikipedia.org/wiki/Octal
2. https://en.wikipedia.org/wiki/Decimal

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I ran bellow commands using the latest version of rust nightly.
• I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• I ran cargo fmt just before my last commit.
• I ran cargo test just before my last commit and all tests passed.
• I added my algorithm to the corresponding mod.rs file within its own folder, and in any parent folder(s).
• I added my algorithm to DIRECTORY.md with the correct link.
• I checked COUNTRIBUTING.md and my code follows its guidelines.

[siriak]

Looks good, thanks!