docs: recommend Renovate instead of Greenkeeper

[brian-smith-tcril]

Most of this ADR is just copied from https://openedx.atlassian.net/wiki/spaces/AC/pages/1841791377/Set+up+Renovate+to+Automate+JavaScript+Dependency+Updates

I also noticed we had both 0007-bundle-size.rst and 0007-typescript.rst. The typescript ADR was showing up as number 8 on the list so I updated the filename to reflect that.

[sarina]

You also need to update the redirects, see https://github.com/openedx/open-edx-proposals/pull/585/files for an example

[sarina]

Addresses https://github.com/openedx/open-edx-proposals/issues/524

[brian-smith-tcril]

@sarina I added a changelog entry and a redirect https://github.com/openedx/open-edx-proposals/compare/b51a7a49a4787df4436c956ccf9d44f0dd4676a3..b989856ddd101feb3917d8791ab1d045d7acbc68 and then fixed a mistake in my redirect https://github.com/openedx/open-edx-proposals/compare/b989856ddd101feb3917d8791ab1d045d7acbc68..506478e9da91dac84817830fe04910572a4ab332

[sarina]

Thanks!!!