Rename `Diversity` value into `Diversity & Inclusion`

I would like to propose we change our Diversity value into Diversity & Inclusion

Here's why:

• In the description of our Diversity value, we mention Diversity and inclusion are fundamental to the success of GitLab.
• Most of the sub-values of our current Diversity value also fits into the topic of Inclusion (Eg. building a safe community, inclusive benefits, inclusive language & pronouns..)
• We should strive for diversity and inclusion at GitLab as https://www.forbes.com/sites/janicegassam/2019/02/04/diversity-without-inclusion-is-useless/#ea3af0256858
• We already have a #inclusion slack channel rather than a #diversity for the purposes of discussing diversity and inclusion. This highlights the importance of this value
• The term Diversity & Inclusion is an industry term. For example, we have a diversity and inclusion partner rather than a diversity partner.