Added dependabot.yml to test updating git submodules.

[rozza]

JAVA-5840

[rozza]

This is a dependabot.yml that will create a pr for updating the git submodules. Its run weekly.

Althought I'm not certain what needs to be done on the github side (if anything) to enable it.

[rozza]

Docs to enable: https://docs.github.com/en/code-security/getting-started/dependabot-quickstart-guide#enabling-dependabot-for-your-repository

[katcharov]

Looks good, but let's let @alcaeus have a look since it's only a few lines. For the instructions, everything is enabled, except "Dependabot version updates", which prompts me to create this PR's file when I click it. Will check settings after merge.

[alcaeus]

LGTM. I haven't used any commit-message options before, but I presume Ross read the docs and knows what he's doing ;)

[rozza]

@katcharov this has now been merged - there may be some github admin settings to change.