Mentor country details

[Disura-Randunu]

Purpose

The purpose of this PR is to fix #155

Goals

To save Country details on Mentor

Approach

Added relations and modified controllers & services to create & update mentors.
Also updated how category was handled in Update mentor route for admins as there were unnecassary type checks

Screenshots

Checklist

• This PR doesn't commit any keys, passwords, tokens, usernames, or other secrets.
• I have read and understood the development best practices guidelines ( http://bit.ly/sef-best-practices )
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

Related PRs

#169
#170

Test environment

Learning

[Disura-Randunu]

@anjula-sack Made the PR for #155
Also updated categoryId handling on previously made admin api to update mentor as there were unnecessary type checks

[Disura-Randunu]

@anjula-sack We may have to make the DB modifications first. otherwise it'll give an error when fetching the mentor details

[anjula-sack]

Thank you! @Disura-Randunu