[PGPRO-12159] Added functions for exploring the pages of the rum index.

[arseny114]

Six functions have been developed to extract information from the pages of the RUM index:

1. rum_metapage_info() -- is used to examine the information that is placed on the meta page (flags: {meta}).
2. rum_page_opaque_info() -- is used to examine information that is placed in the opaque area of the index page (any index page).
3. rum_leaf_data_page_items() -- is used to examine the information that is placed on the leaf pages of the posting tree (flags: {leaf, data}).
4. rum_internal_data_page_items() -- it is intended for viewing information that is located on the internal pages of the posting tree (flags {data}).
5. rum_leaf_entry_page_items() -- it is intended for viewing information that is located on the leaf pages of the entry tree (flags {leaf}).
6. rum_internal_entry_page_items() -- it is intended for viewing information that is located on the internal pages of the entry tree (flags {}).

To extract information, all these functions need to pass the index name and the page number.

Tags: rum