Add Happy numbers problem in "others" category

[louvelbr]

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

References

Issue number : #2832

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Java files are placed inside an existing directory.

[siriak]

Hi, the build is failing with the following error: ./src/main/java/com/thealgorithms/others/HappyNumbersSeq.java:4: error: class HappyNumSeqTest is public, should be declared in a file named HappyNumSeqTest.java
public class HappyNumSeqTest {
^
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

[yanglbme]

Hi @siriak , please review again.

[siriak]

Only a couple of small comments, everything else looks good :)