Prepare Specification for CLDRv45

[aphillips]

Quoting @macchiati:

2. For the spec, the plan is:
   1. Steven Loomis will create a Part 9 .md file, with the right header/footer
   2. For Mar 4, Monday SOD, the minimum would be to add the paragraph to in Create v45 release paragraph #693 and point people to https://github.com/unicode-org/message-format-wg/blob/LDML45-alpha/spec/README.md as containing the contents that will be poured into Part 9.
   3. Steven Loomis can also be consulted on any format questions, Jira, etc. Eg,
   1. The table of contents is created automatically from the headers
   2. Other link anchors can use html format.
   3. That Part 9 contents should be essentially final by 2024 Mar 27, Wed for the public spec Beta. (successive draft versions can be merged to main whenever they are in good shape, and they will show up in HTML shortly thereafter).
   4. We may get feedback during the beta period, but plan on at most editorial changes after spec beta (2024 Mar 27, Wed).

Addison, I'm assuming that you are the POC for these actions, but the work can of course be distributed within the WG. I created a ticket https://unicode-org.atlassian.net/browse/CLDR-17426 for this addition (we use Jira for CLDR tickets). I didn't know which of the many Addison Phillips on Jira you are, so I left it unassigned for now.

[aphillips]

Note that release LDML45-alpha was created for the CLDR-TC call that resulted in the above. We will have an LDML45 release that corresponds to the 27 March document.

[aphillips]

Created LDML45-Tech-Preview branch and tagged it as a release.