Create community program section in docs

What does this MR do?

This MR adds a section about our Community Program Subscriptions to our docs.

We currently have small sections for the GitLab for Open Source and GitLab for Education program on the subscription docs page, but not about the GitLab for Startups program. This MR adds the Startups program. In the future, we also plan on having a non-profit program, so this MR adds the standard Community Programs term we are using as the umbrella for all of these programs.

This MR relates to our Interim Launch Plan, which is part of the Community Relations team's Community Program Efficiency Initiative.

Goals for this MR

• Make sure all current community programs are represented: OSS, EDU, Startups
• Add instructions for how to complete the OSS verification process, complete with images
• Add information about how Support works for these community programs

In the future (a subsequent MR), we may want to add more information about how public projects compare to our program since there's confusion about how users can access our top tier for free. This MR is focused on items needed for the Interim Launch Plan to succeed.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team