add dependabot

[ashuvssut]

closes #1015

[ashuvssut]

@anushbhatia what is your time preference to get the dependabot PRs?

• weekly - 10am - sunday
• daily - 10am
• Give your own preference

We can also add more update configs like these. checkout this link

I have put the important configs. But we can add more if we need

Validate the dependabot.yml code here when needed

[ashuvssut]

more configs are available

• versioning-strategy (auto/ widen/ increase/ increase-if-necessary??)

[anushbhatia]

weekly will be fine

[ashuvssut]

done