CAMEL-16639: lowercase AsciiDoc attributes and related changes

[djencks]

In this PR (not completely in commit order) (some squashing could be appropriate if we agree on all these changes, but the added comments might be useful for future understanding):
Tooling:
95e3200

• generate headers with lowercase attribute names doctitle, attributeid, shortname, and supportlevel. AsciiDoc attribute names are case insensitive and lowercase by default: doctitle is very standard and we shouldn't argue with it.
• Use lowercase doctitle in gulpfile.js
• (Important!) Fix detection of EIP docs so that they are recognized and updated by UpdateReadmeMojo during the main build. The previous code was extremely incorrect and only worked when maven is run in the core/camel-core-engine directory.
  86220d0, 1945dea
• Comment out and remove code that seems to have no purpose other than preventing camel-disruptor-vm-component.adoc from being processed.
  9057c88
• Remove some useless code that updates parts of the component model that aren't used.
  e808961
• Stop adding the useless [[link-name]] to the top of every file. There might be some circumstance in which this header would be useful, but it is ignored in Antora. I verified that removing these makes no change in the generated site.

Manual changes:
0469b9f

• Remove reactive-threadpoolfactory-vertx.adoc from docs since the source was renamed to threadpoolfactory-vertx.adoc in commit bac083b on 31 July 2020
  af64bcb
• Fix doctitle in options partials
  7bef09f
• Fix doctitle in summary docs
  455746f
• Manually update core/camel-main/.../main.adoc including a TODO. Some 'others' pages seem to have corresponding .json files, perhaps we should use them to generate option tables? main.adoc has other problems as well.
  a672559
• Update and add DSL group to dsl/.../kamelet-main.adoc. If this page should not be in the DSL group, someone needs to add a comment explaining why, and why it's in the dsl directory but not the DSL group.
  d1ee6fb
• Manually update other dsl adocs (they aren't automatically updated). Also make the doctitle and shortname reasonably consistent. Also concatenate duplicate supportlevel attributes. Several of these dsl pages were not previously in nav, perhaps this can be reviewed by someone who knows about the actual state of DSL support.
  bbf1cf6
• Manually update properties-component.adoc (no corresponding json file)
  44acb3f
• Expected changes to others nav as a result of previous changes

Generated changes: cb3d52b

and finally
067bf58

• Remove bogus [[link name]] first lines. Some of this would be generated from e808961, but by no means all. Regenerating the docs after this change results in no additional changes.

[zregvart]

Thanks for cleaning this up!